Negotiators taking part in Yemen peace talks in Switzerland agreed Saturday to create a "neutral" committee to monitor the country's crumbling ceasefire even as at least 68 people were killed on the ground, a source close to the talks said.

"There is an understanding over forming a neutral military committee tasked with monitoring the ceasefire," a source close to President Abedrabbo Mansour Hadi's government delegation said.

The development came after the ceasefire, which took effect on Tuesday and was supposed to last a week, was left in tatters after government forces on Friday seized two towns from rebels and their Saudi-led Arab coalition allies accused the insurgents of escalating the conflict by firing ballistic missiles.

As negotiators meeting near the northwestern Swiss city of Biel tried for a fifth day to salvage the ceasefire, at least 68 people were killed in fighting between troops and Shia rebels in northern Yemen Saturday, military and tribal sources said.

The uptick in violence has left the peace talks, scheduled to wrap up with a press conference in Bern Sunday evening, looking increasingly fragile.

UN special envoy for Yemen Ismail Ould Cheikh Ahmed, who is mediating the talks, had on Friday already voiced alarm at the widespread ceasefire violations.

His office said the negotiating parties in Switzerland had created "a coordination and de-escalation committee ... to strengthen adherence to the cessation of hostilities."

The negotiators are scrambling to end the spiralling conflict, which has killed more than 5,800 people since March.

But sources close to both delegations told AFP Saturday afternoon the talks had ended for the day with little progress.

A source close to the delegation representing President Hadi's government said there had been no agreement on the general framework for the talks and no agreement on the opening of humanitarian corridors.

On Thursday, the UN had said that the two sides had agreed to "a full and immediate resumption of humanitarian assistance" in the flashpoint city of Taez in what the UN envoy had called "a major step forward".

But a local relief group, the Humanitarian Relief Coalition, said no UN aid had reached the city, accusing rebels of blocking aid delivery to areas where Hadi loyalists were holed up.

In a letter submitted by the government delegation to the talks Saturday a lawyer in Taez accused the rebels of confiscating aid sent by the UN World Food Programme.

In another move that had been seen as promising, the pro-government forces and rebels completed an exchange of hundreds of prisoners in the southern province of Lahj on Thursday.

But the government delegation source told AFP the sides on Saturday had failed to agree any further such moves.

"There has been no progress in the detainees issue," he said.

A member of the delegation representing both the Iran-backed Houthi Shia rebels and renegade troops still loyal to wealthy ex-president Ali Abdullah Saleh, told AFP it did not expect any agreement on further prisoner exchanges before a sustainable ceasefire had been decided.

Yemen's conflict began in September 2014, when the Houthis advanced from their northern strongholds to occupy the capital Sanaa.

It has escalated dramatically since Saudi-led air strikes against the rebels began in March, with more than 5,800 killed and more than 27,000 wounded since then, according to the UN.