At least three United Nations staff members were killed in Libya after a bomb-laden vehicle exploded this weekend outside a shopping mall in the eastern city of Benghazi, a spokesman for the international body said.

The attack on Saturday occurred even as the country’s warring sides said they had accepted a cease-fire proposed by the United Nations aimed at stopping combat in the capital, Tripoli, during a coming Muslim holiday.

Health officials said the bomb had exploded outside Arkan Mall in the Hawari neighborhood, where people were gathering for shopping a day before the Eid al-Adha holiday. The Benghazi municipal council said the attack had targeted a convoy for the United Nations Support Mission in Libya.

Footage circulated online showed what appeared to be burned United Nations-owned vehicles as thick smoke bellowed into the sky.

No group immediately claimed responsibility for the attack, which came a month after two bomb-carrying vehicles went off in Benghazi, the stronghold of the Libyan National Army, led by Gen. Khalifa Hifter. The July attack killed at least four people and wounded 33 others.

The planned cease-fire would be the first since the army began a surprise military offensive on April 4 aimed at capturing Tripoli, ushering in fierce battles with militias loosely allied with a United Nations-supported but weak administration in the capital.

The site of the attack is close to the mission’s offices. Two of the dead staff members were from Libya and Fuji, and the blast wounded nine others, health officials said. Three United Nations workers were among the wounded, Stéphane Dujarric, a spokesman for Secretary General António Guterres, said in a statement.

“The secretary general extends his deepest condolences to the bereaved families and wishes a swift recovery to all the injured,” Mr. Dujarric said. “He calls on the Libyan authorities to spare no effort in identifying and swiftly bringing to justice the perpetrators of this attack.”

He added that the secretary general had urged “all parties to respect the humanitarian truce during Eid al-Adha and return to the negotiating table to pursue the peaceful future the people of Libya deserve.”

The United Nations Security Council held an emergency meeting late Saturday afternoon after the deadly attack. The assistant secretary general for Africa, Bintou Keita, told members that the blast had taken place in an area “supposedly under full security control” of General Hifter.

Ms. Keita said the attack highlighted “the continued danger of terrorism across the country,” and it confirmed that the latest hostilities were creating a vacuum “easily exploited by radical elements that strive on chaos and violence.”

She said that the United Nations did not intend to evacuate its people from Libya, and she expressed hope that both sides would abide by their commitment to the Eid cease-fire.

The United Nations’ special envoy for Libya, Ghassan Salamé, condemned what he called a “cowardly attack.”

“This attack will not discourage us, nor will it prevent us from carrying on with our duties to bring about peace, stability and prosperity to Libya and its people,” he said in a statement.

Mr. Salamé said the commitment of the parties of the cease-fire in Tripoli sent “an irrevocable message that the blood of Libyans, and U.N. staff” was not shed in vain “in this heinous explosion.”

The battle for Tripoli has killed over 1,100 people, mostly combatants, and has displaced more than 100,000 civilians. Thousands of African migrants captured by Libyan forces supported by the European Union are being held in detention centers.

In recent weeks, the battle lines have changed little, with both sides dug in and shelling each other in the southern reaches of the capital. Fighters have also resorted to airstrikes and attacks by drones. An airstrike last month killed over 50 people — many of them migrants who died when a hangar collapsed on top of them.

Libya slid into chaos after a 2011 uprising that toppled and killed the dictator Col. Muammar el-Qaddafi. Armed groups have proliferated. The country has emerged as a major transit point for migrants fleeing to Europe.

The Libyan National Army is the largest and best organized of the country’s many militias, and has the support of Egypt, the United Arab Emirates and Russia. But it has faced stiff resistance from fighters aligned with the United Nations-recognized government, which is aided by Turkey and Qatar.