New Delhi: The Pakistan government on Thursday stated that any attempt to block or divert water allocated to Pakistan under the Indus Waters Treaty would be considered an “act of war,” adding that its response would span the “complete spectrum of national power” – a pointed reference to the possible use of nuclear weapons.The warning followed a two-hour meeting of Pakistan’s National Security Committee (NSC), convened to formulate a response to India’s measures following the Pahalgam terror attack.On Tuesday (April 22), 26 Indians, and a Nepali national, most of them tourists, were killed by four terrorists at a bustling meadow in the Kashmiri tourist town of Pahalgam. It was the highest toll of civilians in a terror incident in India since the 2008 Mumbai attacks.A day later, India announced that it was suspending the Indus Waters Treaty, revoking visas of all Pakistanis in India, stopping the sole land border trade point, expelling military attaches and downsizing the diplomatic missions.Follow live updates here.‘Complete spectrum of national power’: Pakistan hints at nuclear optionPakistan responded with several reciprocal measures, but its primary concern, it was evident, was over water.In a statement issued by the Prime Minister’s Office, the NSC, Pakistan’s highest national security decision-making body, said it “vehemently rejects the Indian announcement to hold the Indus Waters Treaty in abeyance.”The treaty, it asserted, was a “binding international agreement brokered by the World Bank and contains no provision for unilateral suspension.”The statement described water as a “vital national interest of Pakistan, a lifeline for its 240 million people,” and declared that its availability would be “safeguarded at all costs.”Then, it stated,“Any attempt to stop or divert the flow of water belonging to Pakistan as per the Indus Waters Treaty, and the usurpation of the rights of lower riparian will be considered as an Act of War and responded with full force across the complete spectrum of National Power.”The reference to “complete spectrum of National power” was a not-so-veiled allusion to Pakistan’s nuclear arsenal.Back in 2002, Lieutenant General Khalid Kidwai, then head of the Pakistan Army’s Strategic Plans Division, set out four redlines that could trigger a nuclear response against India. His remarks were cited in a report by the Pugwash Conference, whose delegation had travelled to Pakistan for discussions with senior officials.The third redline identified was “India proceeds to the economic strangling of Pakistan.” The linked footnote noted, “Examples of economic strangling of Pakistan included a naval blockade and the stopping of the waters of the Indus river”.The Indian government on Thursday formally notified Pakistan of its decision to place the Indus Waters Treaty in “abeyance with immediate effect”.In a letter to her Pakistani counterpart, water resources secretary Debashree Mukherjee said that “sustained cross-border terrorism” had created “security uncertainties” that had “directly impeded India’s full utilisation of its rights under the Treaty”.She added that “apart from other breaches committed by it, Pakistan has refused to respond to India’s request to enter into negotiations as envisaged under the Treaty and is thus in breach of the Treaty.”Further, Pakistan on Thursday also suspended all bilateral treaties, including the 1972 Simla agreement. The treaty was signed by India and Pakistan after the 1971 war which led to the creation of Bangladesh, committing both sides to resolve disputes by peaceful means and bilateral negotiations, in line with the UN charter.Also read: Pahalgam: Congress Resolution Names Pakistan, Accuses BJP of ‘Exploiting’ Tragedy to Sow DiscordWhile Pakistan had always claimed that UNSC resolutions were the basis for resolving the Kashmir issue, India has argued that the 1972 Simla Agreement takes precedence, framing Kashmir as a purely bilateral issue and ruling out any third-party involvement.Critically, the agreement explicitly affirmed that the Line of Control established after the 1971 ceasefire must be respected and that neither side should seek to alter it unilaterally.There was no official response from the Indian government to Pakistan’s announcements. However, a background note circulated among political reporters sidestepped the implied nuclear threat and instead highlighted the significance of Pakistan suspending the Simla Agreement, which had obligated both countries to respect the Line of Control. Government “sources” remarked pointedly, “So now, India can also cross the LoC”.Beyond the Kashmir dispute, several bilateral frameworks designed to manage tensions could come under strain. These include arrangements to reduce nuclear risk, such as the exchange of lists of nuclear facilities and advance notice of ballistic missile tests.Other agreements cover the exchange of prisoners and the facilitation of religious pilgrimages, governed by a 1974 protocol that has been periodically updated.The ceasefire agreement along the Line of Control, signed in November 2003, is another key accord. Following a spike in violations, the two sides recommitted to the agreement in 2021, which has since helped maintain relative calm along the frontier.The background note from Indian government sources described Pakistan’s withdrawal from two agreements at reducing nuclear tensions as a “shocking step by Pakistan to threaten the entire world with nuclear apocalypse.”It added that without these frameworks – particularly the agreement on pre-notification of ballistic missile tests – “the risk of such grave misunderstandings will increase”.The note also stated that there was “no reason” to suspend agreements on “practical cooperation in cooperating against drug trafficking, maritime disasters, telecommunication links etc”.India briefs key foreign envoys on security situationIn New Delhi, foreign secretary Vikram Misri briefed ambassadors from the permanent five members of the UN Security Council, along with key partners such as Germany, Japan and Qatar.Official sources confirmed that Chinese envoy Xu Feihong was among those invited for the half-an-hour-long presentation by Misri.The Ministry of External Affairs (MEA) did not release a readout or any details of the briefing. However, it is understood that Misri’s remarks were broadly aligned with the presentation he made before the Cabinet Committee on Security on Wednesday.During the briefing, he reportedly recalled the Chittisinghpura massacre of 35 Sikh villagers in Kashmir, which occurred on the eve of then-US President Bill Clinton’s visit to India in 2000.He reiterated that India would not tolerate terrorism and that those responsible would be brought to justice. However, he did not explicitly state that military action was under consideration.India had also conducted similar briefings in 2019 following the Pulwama attack, urging foreign governments to press Pakistan to act against terror groups.Pakistan rejects Indian allegations, calls them ‘frivolous’In its statement, Pakistan rejected what it called “frivolous” attempts to link the Pahalgam attack to Islamabad. “In the absence of any credible investigation and verifiable evidence, attempts to link the Pahalgam attack with Pakistan are frivolous, devoid of rationality and defeat logic,” the statement said.The Pakistani NSC accused India of using incidents like the Pahalgam attack to manipulate public perception and pursue a “narrow political agenda.” It warned against a “reflexive blame game” and urged an end to what it described as the “cynical exploitation” of regional tensions.“Extremely irresponsible warmongering by Indian state-controlled media, fuelling volatility in the regional calculus is reprehensible, which requires serious introspection,” the statement added.The committee also asserted that “any threat to Pakistan’s sovereignty and to the security of its people will be met with firm reciprocal measures in all domains.” It further pointed to allegations of Indian involvement in assassination plots on foreign soil, referencing recent cases in the United States and Canada. “The international community ought to remain mindful of India’s state-sponsored extraterritorial assassinations or attempts,” it said.Pakistan defence minister Khawaja Asif at a joint press conference with Deputy Prime Minister and foreign minister Ishaq Dar, again claimed on Thursday that Pahalgam was a ‘false flag operation’. Mirroring India’s actions, Pakistan declared the Indian military attachés persona non grata and reduced the Indian High Commission’s staff strength in Islamabad to 30 diplomats. While India had set May 1 as the deadline for these changes, Pakistan said the measures would take effect a day earlier, on April 30.India had also shut down the Integrated Check Post at Attari, following which Pakistan responded by closing the corresponding facility on its side.In additional retaliatory measures, Pakistan announced the closure of its airspace to all Indian-owned or Indian-operated airlines with immediate effect.Indian private carrier Air India and IndiGo announced that due to the closure of airspace, flights to the UK, North America, Europe and West Asia would take a longer route.In 2019, following the Pulwama terror attack, Pakistan shut its airspace for several months to all international civil aviation, after the nuclear-armed neighbours carried out airstrikes across each other’s territory.This time, however, the restrictions apply only to Indian carriers.Indian government sources claimed that while the suspension of overflight rights would affect the commercial interests of some private Indian airlines, the financial impact would be greater on Pakistan, which they said stands to lose revenue from overflight fees.Pakistan also declared a suspension of all trade with India, including goods routed via third countries. While formal bilateral trade had already been suspended since 2019, indirect trade had continued through Gulf states and other neighbouring countries.The sentiment in New Delhi, that was shared informally with media, was that Pakistan had “not thought through” the full implications of these moves, and might not end up suspending all the bilateral agreements as it has declared.On people-to-people ties, Pakistan announced it was suspending SAARC Visa Exemption Scheme (SVES) privileges for Indian nationals, except for Sikh religious pilgrims.This was obviously in response to India’s own measure of barring Pakistani nationals to travel to India under the SVES scheme, which was obviously a niche category. Even as Pakistan’s NSC was in session, India expanded its visa restrictions – suspending all visa services for Pakistani nationals and cancelling all existing visas with effect from April 27. Only medical visa holders were given a brief reprieve, with validity extended until April 29.In a late-night clarification, the MEA stated that the only exemption will be for Pakistani Hindus holding long-term visas.