Mattis, on a one-day visit to Pakistan, said the South Asian nation had made progress in the fight against militancy inside its borders but needed to make more.
“You want us to sniff them out, we will do that. You want us to take action against them, whatever action you propose, we will do that… (but) these hollow allegations are not acceptable.”
Trump is considering whether to withdraw from the 2015 nuclear deal between Iran and six world powers including the US
The Pentagon said previously that there were roughly 8,400 US troops in Afghanistan, under a cap set during President Barack Obama’s administration.
The situation in Afghanistan, having been in a deadlock for more than 15 years has deteriorated rapidly in the last few months.
After Comey’s recent testimony brought to light links between the attorney general and Russia, Sessions says it is important to discuss the matter with the Senate.
The US has been pressing China to rein in its reclusive neighbour North Korea and also condemned the militarisation of islands in the south China sea.
While US officials say more than 100 civilians died in the airstrike, local officials and eyewitnesses estimate the number of deaths to around 240.
Some US officials questioned the benefit of sending more troops to Afghanistan because any number would not be enough to turn the war-torn situation around.
The US defence secretary says Syria had dispersed warplanes and retained chemical weapons, an issue which needs to handled diplomatically.
Officials said it did not appear that the Iran-backed Houthis would come to the negotiating table under the current circumstances and there needed to be more military pressure on the group.
The US has no standardised process for making compensation payments to the families of thousands of Afghan civilians killed in US-led military operations.
According to US officials the structures built on Spratly islands, which already have military air-strips, could be considered a military escalation.
The US military withdrew a ten-year-old video it posted on Friday to prove that the recent Yemen raid on al Qaida was a success.
US Defence Secretary Ash Carter Carter is in Japan to try to soothe anxieties caused by the victory of Trump, who has called for allies to pay more to sustain US forces or face their possible withdrawal.
Fifteen years after the US invaded Afghanistan to topple the Taliban rulers who had harboured al Qaeda militants who attacked the US, the Taliban have made major gains and are estimated to control more territory than at any time since 2001.
Forty-four Afghan troops visiting the US for military training have gone missing in less than two years, presumably in an effort to live and work illegally in the US.
The decision by the Pentagon is a sign that while it sees some progress by Pakistan in its military operations in North Waziristan, much work remains.
The US State Department has publicly said it still supports Afghanistan in ending the conflict through a peace and reconciliation process with the Taliban.