Yemen's warring parties held a new session of peace talks in Kuwait on Saturday under pressure to firm up a fragile ceasefire that went into effect on April 11.

"The meeting has started," Charbel Raji, spokesman for UN envoy Ismail Ould Cheikh Ahmed, told AFP, without providing details.

Ould Cheikh Ahmed told a press conference on Friday that the delegations had "constructive" negotiations and were committed to firming up the ceasefire.

He acknowledged that the truce was still only between 70 and 80 percent respected and said there were violations by both sides.

Sources close to the government delegation said it would submit a complaint listing 260 ceasefire breaches by the rebels on Friday alone.

Rebel delegation spokesman Mohamed Abdulsalam said the priority was to end the fighting that has killed more than 6,800 people and driven 2.8 million from their homes since March last year.

"Stopping the war and all forms of military action is the priority of the Yemeni people and the priority of their representatives," he said on Facebook.

Third city Taez, where forces loyal to President Abedrabbo Mansour Hadi have been under rebel siege for months, has been a particular source of friction.

Three rebels and two loyalists were killed on Saturday in fierce fighting in Kirsh, a town on the main highway to Taez from the southern port of Aden where Hadi's government is based, military sources said.

The government delegation is to press for the swift implementation of a package of confidence-building measures agreed at the last -- abortive -- round of peace talks in Switzerland in December.

They include the release of prisoners and the lifting of blockades and other obstacles to the the delivery of relief supplies.

The warring sides already carried out two prisoner exchanges last month.

The hard-won negotiations in Kuwait opened on Thursday evening following the delayed arrival of representatives of the Shiite Huthi rebels and allied forces loyal to ousted president Ali Abdullah Saleh.