At least 1,000 people protesting against the rule of Muammar Gaddafi have taken to the streets of Tripoli, the Libyan capital, raising fears of fresh conflict between anti-government protesters and loyalist forces.
Protests called by the opposition began on Friday when worshippers streamed out of a mosque in the centre of the city, chanting "Gaddaf is the enemy of God", witnesses said.
"This is the end for Gaddafi. It's over. Forty years of crimes are over," Faragha, an engineer at the protest, told the Reuters news agency.
Pro-Gaddafi forces fired tear gas at protesters, the AP news agency said, saying at least five cannisters were fired at the crowd in the district of Tajoura in the capital.
"They fired teargas. I heard shooting. People are scattering," a reporter from the Reuters news agency in Tajoura said.
Anita McNaught, Al Jazeera's correspondent in Tripoli, said it was not possible to immediately verify the reports, but that there was a heavy security presence in the city.
"There is some evidence that there's been burning tyres, but beyond that it has been essentially a state of lockdown. The shops are shut, the streets are empty, minimal traffic and an extremely high and visible security presence in all major intersections in the city."
Government forces set up checkpoints in Tripoli ahead of the action, and residents said soldiers had been roaming the city in civilians cars.
Some news agencies have also reported a crackdown on foreign journalists, saying security guards have attempted to block their movements. Internet services have also reportedly been disrupted in Tripoli and the eastern city of Benghazi.
Meanwhile, Interpol, the international police agency, has issued an international "Orange Notice" alert for Gaddafi and 15 members of his inner circle to help police around the world enforce UN sanctions.
"The individuals subject to the Orange Notice have been identified as being involved in or complicit in planning attacks, including aerial bombardments, on civilian populations," Interpol said.

Artillery fire

Friday's action comes amid more reports of battles between loyalist forces and anti-Gaddafi fighters in strategic cities.
Heavy shelling and machine gun fire has been reported near Ras Lanuf, the eastern oil port 660km from Tripoli.
The Reuters news agency said rebels fired a sustained barrage of mortar bombs and rockets at a military base in Ras Lanuf on Friday afternoon, which was met with artillery fire from the army.
"There are lots of flames, thuds and bangs. There is the wailing of sirens and puffs of smoke in the air," a Reuters correspondent said.
The AFP news agency said at least four people were killed in the fighting.
Rebels have vowed "victory or death" as they headed towards the oil terminal, with reports that trucks of armed anti-Gaddafi fighters are heading towards the area.
"We're going to take it all, Ras Lanuf, Tripoli," Magdi, an army defector, fingering the pin of a grenade, told Reuters.

Gaddafi forces 'regain control'

At the same time Gaddafi's forces have regained control of az-Zawiyah, 50km from Tripoli, according to state television.
"The people of Zawiyah and the heads of the popular committees have made Zawiyah safe from the armed terrorist forces," Channel One reported on Friday.
Government forces are said to be battling to regain control of rebel-held towns close to Tripoli, trying to create a buffer zone around what is still Gaddafi's seat of power.
Earlier opposition fighters said Libyan forces carried out an air strike near a military base on the western outskirts of Ajdabiya, a town captured by the opposition, but said there was no casualties or damage.
Witnesses said a bomb was dropped on Friday and other rebel fighters say two rockets were fired at the base near the eastern town, but also missed.
Al Jazeera reporters near the town say standstorms have hit the region, making further strikes unlikely.
But Hoda Abdel-Hamid, Al Jazeera's correspondent in the eastern city of Benghazi, said she had heard reports that volunteers going to the front line of fighting were feeling "very vulnerable from the air".
Opposition protesters in the country's east have set up advanced positions 50km west of Brega, which lies in between Gaddafi's hometown of Sirte and the opposition-held port of Benghazi, and sits near ethnic fault lines between tribes loyal to the leader.
Fighters, who are poorly equipped and not well trained, are also said to have pushed further west on Friday, heading along the main coastal road out of Uqayla, a village 280km from Benghazi.