There have been reports of summary executions and abductions of civilians in Mazar-e-Sharif since opposition fighters seized the northern city from the Taliban, U.N. officials said Monday.

The officials said there was no confirmation of the reports and they had no details. It was not known whether the violence involved opposition fighters taking revenge against lingering Taliban or pro-Taliban residents, or involved personal disputes.

U.N. officials also said an opposition commander had seized a U.N. convoy of 10 trucks carrying aid to the area and that a U.N. food warehouse in the city had been looted — though it was not known whether by the opposition or fleeing Taliban fighters.

Lindsey Davies, spokeswoman for the U.N. World Food Program, said the situation in Mazar-e-Sharif "remains volatile, with reports of looting, abduction of civilians from the city, uncontrolled free-lance gunmen, and some street battles are ongoing."

U.N. spokeswoman Stephanie Bunker — who like Davies spoke in the Pakistani capital, Islamabad — said "unconfirmed reports speak of incidents including violence and summary executions" in Mazar-e-Sharif.

After they took Mazar-e-Sharif on Friday, one opposition commander reportedly ordered his forces to restrain themselves and offered an amnesty to Taliban supporters in the city. But several factions of the alliance, which is loosely made up of rival warlords who have opposed in the past, were involved in the city's capture.

Mazar-e-Sharif changed hands several times between the Taliban and opposition in 1997 and 1998, and each time there were bloody massacres allegedly committed by the victors.

Meanwhile, the U.N. Children's Fund said a 10-truck convoy was commandeered by opposition fighters soon after it arrived in Mazar-e-Sharif on Saturday with 200 tons of supplies. UNICEF said in a statement from Geneva that it was trying to "ensure the safety" of the convoy's Afghan drivers and the supplies.

Davies, of the WFP, said about 89 tons of food — including sugar, oil and high energy biscuits — had "disappeared from our warehouse" in Kabul.

UNICEF said its offices in the city had been stripped of their contents, including computers and furniture.

UNICEF and the WFP said they didn't know who was behind the looting of their facilities. But UNICEF said fleeing Taliban forces had made off with all its vehicles and communications equipment.

The northern alliance seized Mazar-e-Sharif on Friday, forcing Taliban soldiers to retreat south toward Kabul — though over the weekend U.S. officials said there were still pockets of Taliban resistance in the city.

The capture of strategic northern city opened up a corridor for badly needed humanitarian aid from neighboring Uzbekistan. But relief officials are waiting to ship aid until they confirm that the area is secure.

The WFP hopes to bring 17,000 tons of food a month into Afghanistan from Uzbekistan. "We have food, staff and offices to help the impoverished Afghans of the northern areas. What we need is security," said Davies.

The United Nations says Afghanistan is in the middle of a humanitarian crisis because of a devastating drought and a protracted civil war.

The opposition has pushed the Taliban out of most of northern Afghanistan in the past few days with the help of heavy U.S. bombing, and has threatened to launch an offensive on Kabul.