Rebel-held Az Zawiyah, just 50 km west of Tripoli, was the subject of a fierce assault by forces still loyal to 68-year-old Muammar Gaddafi. Heavy casualties were reported there and in other key cities, including the eastern port of Ras Lanuf.
Al-Jazeera quoting witnesses said on Saturday that at least 30 civilians were killed after security forces attempted to retake Az Zawiyah that has for days been defying Gaddafi's rule.
The rebellion in Az Zawiyah -- the closest rebel-held territory to Gaddafi's bastion of Tripoli and also the site of an oil refinery -- has been an embarrassment to the Libyan authorities who are trying hard to demonstrate that they control at least the west of the country.
Eastern regions of the country, around the city of Benghazi, have already fallen out of Gaddafi's control after a popular revolt against his 41-year rule which began in mid-February.
In another development, two explosions at a military arms depot outside the rebel-held city of Benghazi, which took place minutes apart, left at least 19 people dead and dozens injured, reports reaching Cairo said.
It was not immediately known what caused the explosions, but hospital sources in Libya's second-largest city said they believed the blasts were not triggered by an air strike by pro-Gaddafi forces in the region.
Gaddafi's warplanes had earlier attacked military bases overrun by rebels, though they had missed their targets.
Clashes briefly erupted after the Friday prayers in the capital Tripoli. Braving the large presence of gun-totting security personnel and mercenaries, over 1,000 protesters hit the streets in large numbers after the Friday prayers, demanding ouster of the Libyan ruler and chanting slogans like "Gaddafi is the enemy of God", witnesses said. They were tear-gassed and fired upon by the forces loyal to Gaddafi.
Media reports said the protesters tore down posters of the Libyan leader and spray-painted walls with graffiti such as 'Down with Gaddafi' and 'Tajoura will dig your grave.'
For the first time since the uprising began on February 15, Interpol issued an Orange Notice against Gaddafi and 15 other Libyans, including members of his family and close associates. The Interpol alert is aimed at ensuring that law enforcement agencies in each of the world police bodies in 188-member countries take all necessary measures to enforce travel ban against the Libyan leader and others.
Fierce fighting was also reported outside Ras Lanuf town, with the sound of multiple explosions and heavy artillery being heard after opposition fighters advanced on the city, BBC said. Pro-Gaddafi forces withdrew to Ras Lanuf two days ago after a battle.
Rebels at Ras Lanuf later told the media they had taken complete control of the town, but there was no independent confirmation. There were also conflicting reports about the situation in Brega. Some government sources were quoted as saying that the town was in rebel hands, while others insisted it was not.
On Friday, Libyan forces carried out an air strike near a military base on the western outskirts of Ajdabiya, a town that fell in the hands of the anti-Gaddafi rebels. However, media reports said there were no casualties or damage.
In Caracas, Venezuela's Foreign Minister Nicolas Maduro said that Libya has given go-ahead to his country to form a mission to find a peaceful resolution to the crisis in the North African country, a day after the US and France rejected the Venezuelan mediation offer. Meanwhile, the United States dispatched its two military aircraft -- under a code-name Operation Odyssey Dawn -- to Tunisia border on Friday evening with relief supplies for thousands of foreigners fleeing Libya.
A day after US President Barack Obama made the announcement, the State Department and Pentagon said two C-130 military transports have landed in Djerba, Tunisia, delivering humanitarian supplies from the United States Agency for International Development. The Pentagon, which has sent considerable air and naval assets to the region along with 400 marines, said it is closely monitoring the situation in Libya.
"We have seen very clearly broadcast reports showing effects of air power being used. Whether or not those were used on rebels, I can't say but there is evidence they have used air assets and dropped ordnance," Pentagon spokesman Col Dave Lapan, told reporters in Washington.
Over one lakh people have fled Libya, where the violence in the uprising against Gaddafi has killed at least 1,000, according to United Nation estimates.
