The five-day humanitarian truce in Yemen ended abruptly Sunday with a series of Saudi-led coalition airstrikes against Shiite rebels, witnesses and security officials told the Associated Press. The ceasefire ended at 11 p.m., local time (4 p.m. EDT).

Rebel positions and tanks in areas of Aden were hit, said officials and witnesses, speaking on condition of anonymity. Saudi Arabia and its allies have been flying sorties against Houthi rebels and forces loyal to former President Ali Abdullah Saleh since late March in a bid to restore ousted President Abed Rabbo Mansour Hadi to power.

The United Nations sought to extend the truce, a request backed by the Yemeni army, at the start of a conference on Yemen convened in Riyadh, Saudi Arabia, Reuters reported. Houthi representatives did not attend.

The ceasefire began Tuesday to allow food, fuel and medicine to be shipped in to alleviate shortages. The U.N. World Food Program said the effort was largely successful.

The World Food Program provided 120,000 liters of fuel and planned to deliver rations for 750,000 people, with most of the supplies moving through Djoubti, the Wall Street Journal reported. Supplies also were airlifted in by the U.N. High Commissioner For Refugees.

Dozens of casualties were reported as a result of fighting in Taiz and elsewhere Sunday amid charges rebels were denying people access to aid, the Yemen Post reported. Houthi militants were reported firing rockets on residences.

Hussein al-Bukhaiti, a pro-Houthi activist, threatened retaliation for the Saudi strikes, the Journal reported. “If the aggression increases, Ansar Allah [Houthis] will declare war on Saudi Arabia,” he said.

The resumption of airstrikes was reported by Saudi television but there was no official confirmation.

Hadi told the Riyadh conference the Houthis were responsible for the conflict and called for international financial and political support.

 “They endangered local, regional and international security,” he said. “They aborted the peaceful transition of power that was agreed upon.”

Rebels took control of Yemen's government in February, forcing Hadi to flee to Saudi Arabia in March.