Hundredvis af demonstranter mod Libyens leder Muammar Gaddafi stødte natten til onsdag sammen med regeringstilhængere og politi, oplyser BBC World news onsdag.
Eyewitnesses told the BBC the overnight unrest followed the arrest of an outspoken critic of the government.
The lawyer was later said to have been released but the protests continued.
Pro-democracy protests have swept through several Arab countries in recent weeks, forcing the leaders of Tunisia and Egypt from power.
A call has been put out on the internet for protests across Libya on Thursday.
Tuesday’s protests began after the arrest of Fathi Terbil, who represents relatives of more than 1.000 prisoners allegedly massacred by security forces in Tripoli’s Abu Salim jail in 1996, reports say.
Sources say he was held after telling relatives of current inmates that the prison was on fire and urging them to protest. Mr Terbil was later said to have been freed.
The reported unrest comes a day before planned anti-government demonstrations on Thursday, which are being organised via the internet.
