Details added (first version posted at 12:36)
NATO planes carried out bombings in Tripoli on Tuesday in what appeared to be one of the heaviest raids since its Libyan air campaign began two months ago, dpa reported.
Government spokesman Moussa Ibrahim said 13 people were killed and 150 injured.
About 20 explosions were heard within a half-hour in the capital, and smoke was seen rising from near leader Moamer Gaddafi's Bab al-Aziziya residence as the attack was answered by Libyan anti-aircraft fire.
The reports came as the British government began considering deploying attack helicopters against targets and forces in Libya.
Armed Forces Minister Nick Harvey said no decision had yet been taken on helicopters, but it was "among a range of capability options under consideration."
Media reports had earlier suggested as many as 18 British and French helicopters would be deployed to support rebel forces.
The deployment of helicopters would step up NATO's involvement in the conflict.
NATO's airstrikes began at the end of March after the UN Security Council passed a resolution ordering the protection of civilians in the conflict.
In its most recent statement, NATO said it had struck a government vehicle storage facility near Gaddafi's Bab al-Aziziya compound. It said Gaddafi's government has used the facility since fighting between rebels and government forces began in February, "resupplying the regime forces that have been conducting attacks against innocent civilians."
Meanwhile, a public health committee in the western city of Misurata said it had buried around 4,000 members of Gaddafi's forces in the city, which saw some of the worst fighting in the country, opposition website Bernieq reported.
Committee head Bashir Al-Tarabulsi said most of the dead had been African mercenaries and Libyan soldiers. He said the bodies had been lying on the streets for over one month.
The committee took photographs of the bodies and compiled lists of the names it could identify, he said.
The opposition, which controls key eastern cities such as Benghazi, says over 12,000 people have been killed in the past three months.
Rebels in the western part of the country said extra forces loyal to Gaddafi took control of the Yefren city centre and the surrounding valley and hills.
"It has become impossible for people to get medication due to the fact that armed Gaddafi forces have taken the hospital and have cut the electricity," witnesses in Yefra told online opposition groups.
In another development, Libya's rebel Interim Transitional National Council (ITNC), based in the eastern city of Benghazi, said it would establish representation in the United States and France.
The ITNC accepted an invitation to open an office in Washington by US Assistant Secretary of State for Near Eastern Affairs Jeffrey Feltman, who is currently visiting Benghazi, Al- Arabiya reported.
The French foreign ministry said the council would soon appoint an envoy to Paris. France was the first country to declare the council the "legitimate representative of the Libyan people."
The council was created in February after weeks of fighting between rebels and forces loyal to Libyan leader Moamar Gaddafi, and describes itself as the "political face of the revolution."