Some 6.7 million people in Yemen are classified in phase 4 on an international scale of food security, with phase 5 constituting a famine.
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.
It was the biggest gathering since a Saudi-led coalition of Arab states entered the conflict in 2015 to try to restore President Hadi to power.
Yemen believes the UN plan legitimises the rebellion against the country’s internationally recognised government.
Diplomats had hoped the Houthis would hold off on putting together a cabinet of their loyalists and instead form a unity government with their Yemeni foes whom they pushed into Saudi exile.
According to John Kerry, Yemen’s Houthi group and the Saudi-led coalition agreed to a ceasefire from Thursday.
The US will review its support for the 18-month-old military push after planes hit mourners at a community hall in Sanaa on Saturday, killing 140 people, according to one UN estimate and 82 according to the Houthis.
At least 20 soldiers were killed in a bomb blast in the capital city of Sanaa.
Sources said the attack targeted a school compound where conscripts of the Popular Committees, forces allied to President Hadi, were gathered for breakfast.
Islamist militants have been gaining foothold in the impoverished country, taking advantage of the chaos around Yemen’s civil war that began in 2014.
UN Secretary-General Ban Ki-Moon urged Yemeni negotiators to end the conflict through compromise, giving the example of the deal between the Colombian government and rebels.
The stability of Yemen, where al Qaeda and Islamic State are vying for influence, is of international concern as the country neighbours Saudi Arabia, the world’s top oil exporter, and is also near key shipping lanes.
The talks, which opened late on April 21, seek a solution to a war that has killed more than 6,200 people and triggered a humanitarian crisis.
Yemen’s warring parties’ conciliatory signals may help end one of the world’s worst humanitarian crises, and defuse tensions between rivals Iran and Saudi Arabia.