The appeal followed clashes between rebels and pro- government forces across south Yemen yesterday despite the truce, which has largely held since it began at 11:00 pm (local time) Tuesday.
"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.
Yemeni political parties began talks today in the Saudi capital aimed at finding a solution to the crisis.
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But the Huthis stayed away from the meeting of about 400 delegates including President Abedrabbo Mansour Hadi, who has taken refuge in Riyadh.
Hadi repeated accusations that the rebels had staged a "coup" and committed abuses against the population.
"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.
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 yesterday 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.
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.