The United Nations envoy for Yemen has hailed a "constructive" first full day of peace talks but called for a halt to air strikes by a Saudi-led coalition and missile fire by Houthi rebels.
Ismail Ould Cheikh Ahmed said firming up an April 11 ceasefire was essential to the success of the negotiations in Kuwait.
The envoy, who spent months getting the warring sides to the negotiating table, said Friday's talks had been "very constructive".
"There was a consensus on strengthening the ceasefire and the two sides were committed to the need to achieve peace and that this is the last opportunity," he said.
The United Nations hopes that the negotiations will end fighting across Yemen that has killed more than 6,800 people and driven more than 2.5 million from their homes since March last year.
The Houthis have held Yemen's capital, Sanaa, since September 2014 and their advance triggered a Saudi-led air campaign in support of President Abd-Rabbu Mansour Hadi's government.
As the talks got under way, military sources told the AFP news agency that the ceasefire was largely holding on the ground, although clashes were continuing around the flashpoint city of Taiz, where pro-government forces have been under rebel siege for months, and in Jawf province on the Saudi border.
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Ould Cheikh Ahmed said the rebels complained of continuing air strikes by the Saudi-led coalition while the government side complained of continued ceasefire violations by the rebels.
He said he had contacted Saudi Arabia about the coalition air strikes and they had said the raids were ordered only in response to ceasefire violations by the rebels.
"The ceasefire is respected between 70 percent to 80 percent all over Yemen," Ould Cheikh Ahmed said.
The talks are based on UN Security Council resolution 2216 which calls for the Houthi fighters to withdraw from areas they seized since 2014 and hand heavy weapons back to the government, the UN envoy said.
Al Jazeera's Hashem Ahelbarra, reporting from the talks, said a major hurdle in the negotiations was a "huge trust deficit" between the warring sides.
"The UN envoy along with the different factions are trying to work on confidence-building measures and start a political process with the aim of forming a national unity government," he said.
"For the United Nations this is a very critical moment. They have to seize the opportunity or there is not going to be peace any time soon."
The war has taken on regional implications, as Sunni-ruled Saudi Arabia accuses regional Shia rival Iran of arming and training the Houthis.
Iran says it only provides the rebels with political support, though the US Navy says its sailors and allies have seized weapons heading for Yemen from Iran.
Source: Al Jazeera and agencies