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 yesterday in the Marib and Taiz provinces to the south, however, according to sources in militias opposed to Iranian-backed Shiite Houthi rebels. Details were not immediately available. The Arab coalition fighting the Iranian-allied Houthi rebels announced a cease-fire from 11:59 p.m. local time on Sunday evening for five days to allow for the delivery of humanitarian aid amid severe shortages of fuel, food and medicine.

The violence prolongs a four-month-old conflict rooted in political strains that spread across the country last year, when the Houthis seized Sanaa and pushed aside now-exiled President Abed Rabbo Mansour Hadi. Four months of air raids and war have killed more than 3,500 people in the Arabian Peninsula state. United Nations children's agency UNICEF said 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 cease-fire 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 makes 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 U.N. about the cease-fire and would not form a position towards 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 Hadi. On Sunday, Yemeni forces allied with the coalition fought Houthi rebels for control of the country's largest air base north of Aden. There was no word on the situation there on Monday. Houthi rebels 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.

Fractious Yemen has remained in turmoil since last September, when the Houthis overran Sanaa, where they sought to extend their influence to other parts of the country. On March 25, Saudi Arabia and its Arab allies began an extensive military campaign targeting Houthi positions across Yemen. Riyadh says its air campaign comes in response to appeals by Hadi for military intervention against the Houthis. The Houthis, meanwhile, denounce the offensive as an unwarranted "Saudi-American aggression" on Yemen.