Attack helicopters struck Moamer Kadhafi's forces on Saturday, NATO said as China made contact with rebels fighting to oust the Libyan leader and Russia prepared to send a mediator.

As the NATO-led war entered a new phase, explosions rattled Tripoli overnight and US lawmakers chided President Barack Obama for failing to obtain congressional approval for military action in Libya.

"Attack helicopters under NATO command were used for the first time," the military alliance said in a statement.

"The targets struck included military vehicles, military equipment and fielded forces" of the Kadhafi regime, it said, without detailing where the strikes had taken place.

British Apache choppers and French Gazelles and Tigres were deployed, the two countries said. The Apaches returned safely to a carrier, Britain's defence ministry said, also without disclosing the targets.

The helicopters destroyed a radar post and a checkpoint near the coastal oil city of Brega in the overnight strikes, according to Britain's domestic news agency PA.

The attacks were launched as part of the aerial campaign to protect Libyan civilians from Kadhafi's forces in line with a UN resolution that barred ground troops.

A spokesman for France's military chiefs, Thierry Brukhard, said the copters destroyed about 20 targets and drew light arms fire from forces on the ground but were not damaged.

"The use of attack helicopters provides the NATO operation with additional flexibility to track and engage pro-Kadhafi forces who deliberately target civilians and attempt to hide in populated areas," said a NATO statement.

On the diplomatic front, China said its ambassador to Qatar, Zhang Zhiliang, held talks with Mustafa Abdul Jalil of the rebels' National Transitional Council in recent days to discuss the conflict in the oil-rich nation.

"The two sides exchanged views on the Libyan situation," foreign ministry spokesman Hong Lei said.

"China's position on the Libyan issue is clear -- we hope that the Libyan crisis can be resolved through political means and that the future of Libya is decided by the Libyan people."

Russian President Dmitry Medvedev said Moscow would send an envoy to Tripoli and the rebels' capital of Benghazi to mediate, the Italian news agency ANSA reported, quoting diplomats.

"We would like as much as possible for the problem to be resolved through negotiations and not by military means," said Medvedev.

Interfax news agency quoted the envoy, Mikhail Margelov, as saying he would travel to Benghazi on Monday "to meet representatives of the opposition and a number of other political forces in Benghazi."

Since February, Kadhafi's forces have been embroiled in a battle with rebels looking to put an end to his more than four decades in power.

The US House of Representatives, meanwhile, approved a vote that rebuked Obama for maintaining a role in the NATO mission while ignoring Congress, but stopped short of calling for an end to the mission.

The measure calls for a report from the White House within 14 days explaining US objectives, associated costs, the expected duration of involvement and an explanation about why Obama's failure to seek congressional permission.

Washington accused Qatar of violating humanitarian norms by deporting to Benghazi Iman al-Obeidi, a Libyan woman who charged she had been raped by Kadhafi's soldiers.

State Department deputy spokesman Mark Toner said the United States was "disappointed at her forced return" to Libya, which "we believe it's a breach of humanitarian norms."

In Geneva, the UNHCR also slammed Qatar's decision to send Obeidi back, saying it "violates international law."

Obeidi attracted international media attention when she stormed into Tripoli's Rixos hotel on March 26, threw open her coat to reveal scars and bruises on her body to expose her ordeal.

But as she screamed: "Film me, film me, show the whole world all they did to me," she was dragged off by security guards amid scenes of mayhem as journalists were shoved aside while trying to intervene.

A Libyan rebel official told AFP last month that Obeidi had escaped from Libya to Qatar with the help of rebels.

Off Tunisia's coast, up to 270 migrants were missing after a ship packed with refugees fleeing Libya and headed for Italy capsized, Tunisian authorities said.

Rescuers lifted 570 people off the overcrowded vessel after it ran aground and overturned near Tunisia's Kerkennah islands on Wednesday, but between 200 and 270 were still missing, Tunisia's official TAP news agency said.