Peace talks between Yemen's warring factions are on hold pending the arrival of rebel representatives to the UN-backed negotiations, diplomats told AFP on Thursday.

The talks were initially scheduled to start on Monday, and any further delay could dash hopes of ending Yemen's war after the government delegation threatened to pull out if meetings did not begin immediately.

"According to the latest information, the rebel delegation should arrive in Kuwait by the end of the day," said one diplomat close to the talks.

"As a result, the talks could be delayed further until Friday," another diplomat said.

On Wednesday, UN spokesman Stephane Dujarric said negotiations would begin in Kuwait on Thursday.

The rebels only agreed to join the talks after they said they received assurances from the United Nations that pro-government forces would respect a ceasefire which has been violated by warring parties since it came into effect on April 11.

There was still no word Thursday from the rebels on their expected time of arrival.

Representatives of the Iran-backed Huthi insurgents and their allies left Sanaa on Wednesday for Oman and they are expected to continue on to Kuwait.

But they were still in Oman on Thursday morning, according to diplomats.

In Yemen itself, fighting wore on on several fronts, military sources said, as each side blamed the other for truce breaches.

The rebels late on Wednesday fired a Katyusha rocket on the loyalist-held city of Marib, east of the capital, according to an AFP journalist there.

Pro-government military sources reported heavy fighting in Nahm, northeast of Sanaa, as well as sporadic clashes in the northern Jawf province, Taez in the southwest, and central Baida province.

The rebels meanwhile claimed on their sababnews.net website that a Saudi-led coalition fighting them in support of the Yemeni government carried out two air strikes on Nahm and flew sorties over Sanaa, Marib, and Jawf.

The talks are the most important attempt yet to resolve Yemen's devastating conflict, which the UN says has killed more than 6,400 people and forced almost 2.8 million forced from their homes.