British and French attack helicopters struck military targets in Libya for the first time Saturday as NATO tried to ratchet up the pressure on the country’s leader, Moammar Gaddafi, a few days after extending its mission for three more months.

The British Apache and French Tiger and Gazelle helicopters rained missiles and cannon fire on targets behind the front line near the eastern oil city of Brega, according to military officers from both countries. They said targets included military vehicles, military command buildings, a radar installation and a checkpoint.

The helicopters’ deployment represents a calculated risk, giving NATO the ability to strike military targets in built-up areas with more precision than fast-moving, high-flying warplanes but, since helicopters are more vulnerable to ground fire, also raising the risk of the first Western military casualties of the campaign.

British Defense Secretary Liam Fox denied that the move was an admission that jets had failed to achieve the alliance’s ultimate objective — forcing Gaddafi from power. “It’s not Plan B at all,” Fox told a conference in Singapore. “The use of attack helicopters is a logical extension of what we had already been doing. We already had fast jets in action; this gives us a chance to target new targets in a way we weren’t able to do.

Hours after the helicopter attack, British Foreign Secretary William Hague and International Development Secretary Andrew Mitchell arrived in the rebels’ de facto capital, Benghazi, to meet with officials there.

“As long as Gaddafi continues to abuse his people, we will continue and intensify our efforts to stop him from doing so,” Hague told a news conference, news agencies reported.

In a reminder to the rebels that they could not rest on their laurels, Hague and Mitchell also “stressed the importance of developing plans for a competent, inclusive and transparent administration that includes clear civilian control of military and regional representation,” the British Foreign Office said in a statement.

Gaddafi’s government has suffered several setbacks in the past week, including the defection of its oil minister and several senior military officers and the largest protests in nearly three months in the capital, Tripoli. Yet the rebels admit there is little sign of cracks in Gaddafi’s inner circle.

After weeks of swinging back and forth, the main coastal front line in the conflict has settled just to the east of the strategic city of Brega, which lies 482 miles east of Tripoli and remains under Gaddafi’s control.

Oliver Miles, former British ambassador to Libya, told The Washington Post that despite the deployment of attack helicopters, the conflict could drag on. “My military friends tell me this is not very effective, that this kind of fighting is not going to be controlled from the air,” he said.

There was no immediate comment from the Libyan government, but the head of the rebel Transitional National Council in Benghazi, Mustafa Abdel Jalil, said the rebels “welcomed any measures to expedite the departure of Moammar Gaddafi.”

To the west, rebel fighters in the besieged city of Misurata welcomed the news of the NATO move and said they hoped to see the helicopters neutralize the heavy artillery they said was impeding their advance.

“We can win this battle,” said Abu Mohammed, one of the fighters. “We have no problem if we face Gaddafi’s forces, but they are not facing us, they are shelling from a distance.”

While the coastal front line is relatively static, the rebels have made progress in the western Nafusa mountain range, winning control of four towns Friday, the Associated Press reported.

The small rebel force in the sparsely populated region is unlikely to threaten Gaddafi’s hold on Tripoli, but the victories could bring relief to local residents by opening up roads between their communities.

In what has become an almost daily occurrence, NATO aircraft also hit Tripoli on Saturday evening. At least six powerful explosions were heard.

Special correspondent Portia Walker in Misurata contributed to this report.