SANAA (Reuters) - A truce appeared to be holding on Monday in Yemen's capital Sanaa, the target of near-nightly air raids during a fourth-month-old war, with residents saying the city had passed a quiet night.
There were clashes early on Monday in Marib and Taiz provinces to the south, however, according to sources in militias opposed to Houthi forces. Details were not immediately available.
The Arab coalition fighting the Iranian-allied Houthi militia announced a ceasefire from 11.59 p.m. (2059 GMT) on Sunday evening for five days to allow for the delivery of humanitarian aid amid severe shortages of fuel, food and medicine.
Four months of air raids and war have killed more than 3,500 people in the Arabian Peninsula state. U.N. children's agency UNICEF says the death toll includes 365 children.
Aden and other southern provinces have been largely inaccessible to U.N. food aid, and about 13 million people - more than half the population - are thought to be in dire need of food.
U.N. Secretary-General Ban Ki-moon welcomed the ceasefire and urged all parties to suspend military operations during the pause and refrain from exploiting it to move weapons or seize territory.
In a statement late on Sunday, Ban said he "appeals to all parties to exercise maximum restraint in cases of isolated violations and to avoid escalation."
"The growing number of civilian casualties, including the disturbing reports of civilian deaths in Mokha on Friday evening, in the unfolding humanitarian catastrophe make a pause and an eventual extension an imperative."
He was referring to a coalition air strike in western Yemen in which 80 people, mostly civilians, were killed, according to the Houthi-controlled Saba news agency.
Shortly before Ban's statement was issued, the head of the Houthi supreme revolutionary committee, Mohammed Ali al-Houthi, said in comments carried by Saba that the group had not been notified by the United Nations about the ceasefire and would not form a position toward it until then.
The Saudi-led coalition began a campaign on March 26 to reverse months of advances by the Houthis after they moved from their northern stronghold last year, capturing the capital Sanaa and pushing south to the port city of Aden.
The coalition, allied with southern secessionist fighters, retook much of Aden last week in the first significant ground victory in their campaign to end Houthi control and restore exiled President Abd-Rabbu Mansour Hadi.
On Sunday, Yemeni forces allied with the coalition fought Houthi militia for control of the country's largest air base north of Aden. There was no word on the situation there on Monday.
Houthi fighters and army units loyal to former president Ali Abdullah Saleh captured Aden at the outset of the war, prompting Hadi to flee to Saudi Arabia, an ally along with the United States.
(Reporting by Mohammed Ghobari; Writing by Hadeel al Sayegh; Editing by William Maclean and Hugh Lawson)