Libya: Nato steps up air strikes on Tripoli
Nato planes have launched a series of air attacks on Libya's capital, Tripoli, the heaviest so far of the campaign, correspondents say.
Libyan officials say three people were killed and dozens injured in an attack on the barracks of the popular guard.
The strikes came after France announced it and the UK would also deploy attack helicopters to escalate strike power.
Nato is enforcing a UN resolution to protect Libyan civilians, following the uprising against Col Gaddafi's rule.
Meanwhile United States Assistant Secretary of State Jeffrey Feltman, who is visiting the rebel-held city of Benghazi, said the rebels had accepted an invitation to open a representative office in Washington, AFP news agency reported.
Mr Feltman is the most senior US diplomat to visit the rebels.
The US has insisted that Col Gaddafi step down, but has not granted full recognition to the rebel administration - the Transitional National Council.'Bombing and killing'
Thunderous explosions shook the city; as one strike ended, more jets were heard overhead coming in for the next, says the BBC's Andrew North in Tripoli.
Nato says it bombed a vehicle depot next to Col Gaddafi's Bab al-Aziziya compound which had been used by his forces in attacks on civilians.
The move to use attack helicopters marks a significant escalation of the campaign in Libya, and a stepping-up of Nato's pressure on Col Gaddafi and his forces after weeks of near stalemate.
French Foreign Minister Alain Juppe confirmed 12 French Tiger and Gazelle helicopters were being sent to offer Nato a more precise means of striking Col Gaddafi's troops. Most of his soldiers have shed their uniforms, and are using civilian vehicles.
The UK's Apache attack helicopters would deploy from HMS Ocean, the Royal Navy's largest warship. The Army Air Corps' Apaches have been used extensively in Afghanistan, and are seen as effective and potent weapons which can get in close to smaller targets - even in built-up areas such as Misrata.
However, helicopters are more vulnerable to being hit by rocket-propelled grenades or heavy machine-gun fire, so will need to be deployed carefully to reduce those risks.
"This facility is known to have been active during the initial regime suppression of the population in February 2011 and has remained so ever since; resupplying the regime forces that have been conducting attacks against innocent civilians," the alliance said in a statement.
But the Libyan government says it was a base for a reserve military force that was hit and there were casualties among civilians living nearby.
Libyan government spokesman Moussa Ibrahim said three people were killed and 150 wounded in the strikes.
"This is another night of bombing and killing by Nato," he said, quoted by Reuters news agency.
Our correspondent was escorted to a Tripoli hospital where he was shown three bodies with shrapnel wounds as well as several lightly injured people.
People poured onto Tripoli's streets after the bombing was over, our correspondent adds, chanting support for Col Gaddafi and denouncing the Nato alliance.
The attacks came after French Defence Minister Gerard Longuet confirmed media reports France was deploying attack helicopters to Nato's Libya mission.
French Foreign Minister Alain Juppe said 12 Tiger- and Gazelle-type helicopters were being despatched to Libya.
He also said Britain would send helicopters. He said both countries would deploy the new forces as soon as possible.
The UK has yet to confirm the deployment.
Earlier, France's Le Figaro newspaper said the 12 helicopters had been despatched on the French carrier Tonnerre on 17 May.
BBC defence correspondent Caroline Wyatt says the BBC understands the use of the UK's Apache helicopters was authorised by UK Prime Minister David Cameron at a meeting of the National Security Council.
Nato jets have been targeting Col Gaddafi's military infrastructure, but have been unable to stop the fighting.
Rebels control much of Libya's east, while Col Gaddafi's forces control most of the west of the country.
The rebellion against his rule began in February, spurred on by uprisings in Tunisia and Egypt that saw the presidents of those countries overthrown.