Libyan government forces shot down two U.S.-built helicopters being used by rebel forces in the east of the country, the deputy foreign minister said early on Sunday.

Khaled Kaim also slammed the international community for allowing rebel forces to operate aircraft despite the existence of a no-fly zone over the country following U.N. Security Council resolution 1973.

"A clear violation was committed by the rebels to resolution 1973 relating to the no-fly zone. The rebels used two Chinook helicopters and they were shot down" near the eastern oil facilities of Brega, he said. "We have a question for the allied forces _ is this resolution made for the Libyan government only or everyone in Libya?"

The report could not be confirmed with the rebels, but journalists in the area did describe seeing at least one helicopter apparently fighting for the rebels in the area Saturday, though it lacked the distinctive double rotor design of Chinook and appeared to be a Russian built model.

Most aircraft used by the Libyans, whether government or rebel forces, are Russian made, however, but the Directory of World Air Forces from 2008 says Libya had 20 Chinooks, which are used primarily for transport and heavy lifting, in service.

While the Libyan government forces still possess most of the military aircraft in the country, a few were taken by the rebels when some air force units defected in the east of the country following popular uprisings against Moammar Gadhafi's four decades of rule.

NATO, which enforces the no-fly zone said it has been has been applying it to both sides and on Saturday intercepted a rebel MiG-23 fighter jet and forced it back to the airport.

NATO forces also continue to carry out airstrikes against Gadhafi's forces, destroying 17 tanks and damaging nine others, the alliance announced Saturday.

Rebels have criticized the NATO for not giving them sufficient battlefield support as government forces continue to push into the east.

On Saturday, as rebels attempted to advance toward the oil city of Brega, they were flanked by government forces, sending them scrambling back to defend the key city of Ajdabiya. By the end of the day, the two sides were battling each other in the city streets.

On Saturday, fighting continued over the city, with fleeing civilians reporting both sides shelling each other.

At least 11 people died in Saturday's fighting, reported Ajdabiya hospital supervisor Mohammed Idris, with two more rebels killed Sunday.

Recapturing the Ajdabiya would give the Libyan military a staging ground to attack the rebels' main stronghold, Benghazi, about 100 miles (160 kilometers) farther east along the coastal highway. Gadhafi's forces were approaching Benghazi when they were driven back by the international air campaign launched last month to protect civilians and ground Gadhafi's aircraft.

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Associated Press writer Sebastian Abbot contributed to this report from outside Ajdabiya, Libya.