Amnesty International says a man was shot dead when security forces opened fire in the city of al-Bayda.

Police and protesters also clashed in Zentan and Benghazi, where one witness said at least 16 people are believed to have been killed.

This week's protests are the first in Libya, where dissent is rarely allowed.

Pro-government activists were also out on the streets in the capital, Tripoli. They shouted slogans in support of Libya's leader, Muammar Gaddafi.

Pro-democracy protests have recently swept through several Arab nations, with the presidents of Tunisia and Egypt forced to resign amid growing unrest.