TRIPOLI, Libya -- British jets hit a military barracks in the Libyan capital early Sunday, intensifying NATO pressure on Libyan leader Muammar Qaddafi nearly four months into an uprising to end his erratic 42-year rule.
The airstrikes on the barracks -- repeated targets of NATO strikes -- followed the Western alliance's first use of attack helicopters Saturday.
By intensifying attacks from the air and using helicopters to target government forces who melt into the civilian population for cover, NATO is providing a major boost to Libyan rebel forces who have seized much of the country's east and toeholds in the west.
Emboldened rebels in recent days have forced government troops from three western towns and broke the siege of a fourth.
A government official, speaking on condition of anonymity because he was not authorized to speak to reporters, said the Sunday strikes caused no casualties because the barracks were abandoned after having come under repeated NATO attack.
A NATO official, however, said Royal Air Force Tornados fired eight missiles into a surface-to-air missile depot in Tripoli. The early Sunday attacks also hit military sites in the town of Tajoura, west of Tripoli.
Saturday's strikes by French and British helicopters targeted Libyan troops hiding in populated areas, as well as military vehicles and equipment -- targets often unavailable to higher-flying jet fighters.
Lt. Gen. Charles Bouchard, commander of the Libya operation, said the engagement "demonstrates the unique capabilities brought to bear by attack helicopters."
Until Saturday, NATO had relied aircraft that typically fly above 15,000 feet -- nearly three miles. The jets primarily strike government targets but there have been cases when they missed and hit opposition forces by mistake.
The helicopters give the alliance a key advantage in close combat, flying at much lower altitudes.
At a regional security conference Sunday in Singapore, Russian Deputy Foreign Minister Sergei Ivanov said NATO is "one step" from the start of ground operations in Libya.
Russia abstained from a United Nations Security Council resolution vote in March to impose a no-fly zone over Libya. Ivanov said there has been disagreement over how to interpret the scope of the resolution.
In the Saturday attacks, British Apaches hit two targets near the eastern oil town of Brega, according British Maj. Gen. Nick Pope, and separate Royal Air Force planes destroyed another military installation near Brega and two ammunition bunkers at the large Waddan depot in central Libya.
French Gazelle and Tiger helicopters struck 15 military vehicles and five military command buildings, said Col. Thierry Burkhard. All the helicopters returned safely, the French and British said.
Brega is of strategic importance to Libya's oil industry and lies on the Mediterranean coastal road to the capital.
In the early days of the uprising against Qaddafi, Brega shifted between rebel and loyalist hands, but later the front line settled to the east of the town and under government control.
Qaddafi's regime has been slowly crumbling from within. A significant number of officers and several Cabinet ministers have defected, and most have expressed support for the opposition. But Qaddafi shows no signs of leaving power.
Qaddafi has been seen in public rarely and heard even less frequently since a NATO airstrike on his compound killed one of his sons on April 30. That has led to speculation about the physical and mental condition of the 69-year-old dictator, who has ruled Libya since 1969.
Associated Press writers Hadeel Al-Shalchi in Benghazi, Alex Kennedy in Singapore, David Stringer in London, Jamey Keaten in Paris and Don Melvin in Brussels contributed to this report.