Libya’s capital shook with at least 15 massive explosions Tuesday morning, as NATO launched its largest airstrike to date on the heart of Moammar Gaddafi’s regime.

The strike came hours after French officials said Monday that France and Britain planned to deploy attack helicopters to Libya. Such a move would allow greater accuracy in military action within cities but would probably put their troops at higher risk.

NATO planes and ships have been striking cities and military installations in Libya since mid-March. Allied military officials have spoken in recent weeks of the need for escalation to help protect Libyan civilians and have called for Gaddafi to step down.

Allied officials have expressed worry that the situation in Libya would become a stalemate, with Gaddafi remaining in power in the west, rebels controlling the east, and a contested area in between.

Libyan officials have said that NATO is picking sides in a civil war and complained that strikes on Gaddafi’s Tripoli compound are attempts to assassinate the leader of a sovereign country.

The French defense minister, Gerard Longuet, told reporters in Brussels that the helicopters would be used against Libyan military equipment while trying to avoid civilian casualties, the Associated Press reported. Longuet said British military officials were on “exactly the same wavelength” as the French.

The overnight bombings appeared concentrated on Gaddafi’s compound in Tripoli. NATO said in a statement that it had struck a vehicle storage facility adjacent to the compound.

“This facility is known to have been active . . . resupplying the regime forces that have been conducting attacks against innocent civilians,” NATO said.

Government spokesman Moussa Ibrahim said NATO had targeted the headquarters of the military reserves, killing at least three and injuring dozens. He said that the casualties would have been higher except that the government had long ago emptied the headquarters, expecting that it would be hit.

Still, he said, “we’ve never had such an injured number of people.” Gaddafi, he said, was still alive.

Flashes lit up the Tripoli sky near the compound, followed by explosions and shockwaves that shook windows at a hotel a mile away. Anti-aircraft gunfire punctuated the quiet in between the strikes, and an acrid smell filled the air.

At Tripoli Central Hospital, where government minders took journalists shortly after the blasts, about a dozen injured people moved through a ward, many appearing to have light or moderate injuries to their limbs. All were men and were wearing civilian clothing. Most appeared to be in their twenties or thirties.

In another room were three dead men. They were covered in dust. Each man’s head was partially blown away. Their bodies, though cut and bruised, were not damaged nearly as much.

Libyan rebels got another boost Monday when Jeffrey D. Feltman, U.S. assistant secretary of state for Near Eastern affairs, visited their de facto capital of Benghazi, in the eastern part of the country.

State Department spokesman Mark Toner said Feltman would address questions Tuesday about legally recognizing the rebels as the legitimate leaders of Libya but played down the possibility of a major policy change.

“We believe the [rebel Transitional National Council] is a very credible voice for the Libyan people, and we’re strengthening our contacts and deepening them,” Toner said. “But while recognition remains on the table, an option, we’re not there yet.”

In the meantime, he said, the administration would work with Congress to pass legislation to free up frozen Libyan assets for the rebels.

Longuet told reporters that France would use Gazelle helicopters, the Associated Press reported. During fighting in Misurata, a rebel-held city in western Libya that is under siege by government forces, the Libyan military moved into crowded areas, making it difficult for NATO to strike targets without risking significant civilian casualties. Helicopters would make it easier to attack military forces in those situations.

Improved accuracy is the goal of the helicopter deployment, French Foreign Minister Alain Juppe told reporters in Brussels.

No NATO military personnel have died in Libya during the operation, and there have been relatively few civilian deaths, something that even Libyan officials privately acknowledge.

In response to a question about helicopters, a spokesman for the French Defense Ministry, speaking under European ground rules that do not allow the use of names, said that a ship had been deployed to the Mediterranean on May 17, but provided no specifics.

Western officials have called in recent weeks for putting greater pressure on the Libyan government, and Britain’s foreign secretary, William Hague, said at a news conference in London on Monday that “Britain is committed to intensifying military, economic and diplomatic action against the Gaddafi regime in the coming weeks.” He declined to comment about helicopters.

Staff writer Joby Warrick in Washington and special correspondent Karla Adam in London contributed to this report.