SANAA - A UN envoy called for an extension of a five-day humanitarian ceasefire in Yemen due to expire on Sunday as the Huthi rebels boycotted political talks in Riyadh.

"I call on all parties to renew their commitment to this truce for five more days at least," UN envoy to Yemen Ismail Ould Sheikh Ahmed said in the Saudi capital. "This humanitarian truce should turn into a permanent ceasefire," the Mauritanian diplomat added.

"We are trying to regain our nation" from militias backed by "external" forces, he said in a reference to Iran, which has denied arming the rebels.

An Iranian aid ship bound for Yemen in defiance of US warnings has entered the Gulf of Aden and is expected to reach port on Thursday, media in Tehran reported.

The ship's mission has been overshadowed by US calls for it to head to a UN emergency relief hub in Djibouti instead of docking in the Yemeni port of Hodeida.

Clashes raged overnight Saturday in the central city of Taez between rebels - supported by troops loyal to ousted president Ali Abdullah Saleh - and pro-Hadi forces.

The rebels, who seized the capital Sanaa in September and have since swept across many other regions, bombed a village south of Taez city, killing 14 civilians, a local official said.

Sporadic clashes also continued in Aden, which has been the scene of fierce fighting since rebels advanced on the southern port city in late March after Hadi took refuge there.

The United Nations has expressed deep concern about the civilian death toll from the Saudi-led bombing as well as the humanitarian impact of an air and sea blockade imposed by the coalition.

It says more than 1,600 people have died in the conflict since late March.

Some aid has trickled into Yemen since the pause in fighting, but residents of areas where clashes persist complain they remain without the most basic supplies.

The UN children's agency (UNICEF) said in statement that it was "distributing critical humanitarian aid for hundreds of thousands of children and affected civilians across Yemen".

"In the past four days of the pause, UNICEF has prepositioned supplies in health offices and centres which will provide primary health care to over 24,000 people and treat 3,500 severely malnourished children," it said. But in the south, "distribution and services have been slow as a result of the continuing violence."

Residents of Sanaa have echoed calls to extend the ceasefire.

"We don't care about food or water as much as we need security. We hope that this truce becomes permanent," said Umm Hisham. But in the southern city of Daleh, people complained that the rebels have exploited the lull to expand their control.

"The Huthi militia exploited the ceasefire to bomb citizens... We want coalition forces to resume attacks on these militia," said Ali al-Assmar. "We are not benefiting from the truce. The humanitarian aid for Daleh was confiscated by Huthis and Saleh forces," he said.

The Huthis are boycotting the three-day meeting in Riyadh, insisting on holding the talks in Yemen. Yemen's Vice-President Khaled Bahah told AFP that, despite their absence on Sunday, he expected the Huthis would attend future talks. "They have chosen to be out of this conference but, at the end, they will be coming," he said.

Several representatives of Saleh's General People's Congress party were present.

Among the goals of the meeting is working towards a constitution which would be presented to the Yemeni people, "and to hold a referendum to put the results of the dialogue into practice," according to Abdulaziz al-Jaber, head of the conference's organising committee.