Libyan government forces bombed fuel depots in the rebel-held city of Misurata early Saturday, causing a massive conflagration that threatened key sources of electricity and fuel for the besieged city, residents said.

The city is the rebels’ only major base of power in western Libya, and it has been a scene of fierce back-and-forth fighting for months. Residents said the fuel depots were hit shortly after midnight Saturday, and some said they had heard helicopters — a violation of the NATO-imposed no-fly zone blanketing the country, if true. The reports could not be independently confirmed.

“Where’s the NATO?” said a doctor at Misurata’s hospital, who was reached via Skype and spoke on the condition of anonymity to protect his safety. “We are a little bit surprised.”

The doctor said that despite nighttime attacks by Libyan leader Moammar Gaddafi’s forces, there had been no deaths and very few injuries in the city over the past few days. But he said he worried that the strikes on the fuel depots could threaten supplies for the generators that the hospital uses to maintain electricity.

Speaking in the rebels’ eastern stronghold of Benghazi on Saturday, the vice chairman of the opposition Transitional National Council, Abdul Hafidh Ghoga, also said there had been pro-Gaddafi helicopters in Misurata.

Ghoga said Friday that Italy had agreed to supply the rebels with arms, a claim denied by the Italian Foreign Ministry.

Amnesty International has said the attacks on Misurata could amount to war crimes. Amnesty International, Human Rights Watch and Misurata residents say they have seen evidence of cluster bombs being used on the city. The Libyan government has denied using such weapons.

In Benghazi, Ghoga announced that the rebels have appointed part of the committee they want to run Libya if they prevail. The committee would be led by Mahmoud Jibril, one of the top leaders of the Transitional National Council.

Walker, a special correspondent, reported from Benghazi.