Activists using Facebook and Twitter have called for nationwide demonstrations on Thursday to call for Gadhafi's ouster, a constitution and comprehensive political and economic reforms.

Tuesday's demonstration began in front of the local security headquarters after Libyan troops raided the house of rights advocate Fathi Tarbel in Benghazi and took him away, according to a Switzerland-based activist Fathi al-Warfali.

Tarbel was released after meeting with a powerful Libyan security official, Abdullah al-Sanousi, but the protesters proceeded to march through the coastal city to the main downtown plaza, he said.

Independent confirmation was not possible as the government keeps tight control over the media, but video clips posted on the Internet showed protesters carrying signs and chanting: ''No God but Allah, Moammar is the enemy of Allah'' and ''Down, down to corruption and to the corrupt.''

Police and armed government backers quickly clamped down, firing rubber bullets and dousing protesters with water cannons.

Another video with the same date people running away from gunfire while shots are heard. A young man in a white, bloodstained robe was then shown being carried by protesters.

A Libyan security official, speaking on condition of anonymity because he wasn't authorized to release the information, said 14 people, including 10 policemen, were injured. He said protesters were armed with knives and stones.

The outbreak of protests in Tunisia, Egypt, Yemen, Bahrain and Iran has roiled the Middle East and brought unprecedented pressure on leaders like Gadhafi who have held virtually unchecked power for decades.

It also has posed new challenges for the United States, which has strategic interests in each of the countries. President Barack Obama conceded Tuesday he is concerned about the region's stability and prodded governments to get out ahead of the change.

Libya's official news agency did not carry any word of the anti-government protests. It reported only that supporters of Gadhafi were demonstrating Wednesday in the capital, Tripoli, as well as Benghazi and other cities.

JANA, the official news agency, quoted a statement from the pro-Gadhafi demonstrators as pledging to ''defend the leader and the revolution.'' The statement described the anti-government protesters as ''cowards and traitors.''

The government also planned to free Wednesday 110 Islamic militants who were members of a group plotting to overthrow Gadhafi, although it was not clear if the previously scheduled release would occur.

Seif al-Islam Gadhafi, the leader's son, has orchestrated the release of members of the Libyan Islamic Fighting Group, which is suspected of having links to al-Qaida, in the past as part of a reconciliation plan.

Gadhafi, long reviled in the West, has been trying to bring his country out of isolation, announcing in 2003 that he was abandoning his program for weapons of mass destruction, renouncing terrorism and compensating victims of the 1986 La Belle disco bombing in Berlin and the 1988 bombing of a Pan Am airliner over Lockerbie, Scotland.

Those decisions opened the door for warmer relations with the West and the lifting of U.N. and US sanctions, but Gadhafi continues to face allegations of human rights violations in the North African nation.

The activist's arrest followed the collapse of talks between the government and a committee representing families of hundreds of inmates killed when security forces opened fire during 1996 riots at Abu Salim, Libya's most notorious prison. The government has begun to pay families compensation, but the committee is demanding prosecution of those responsible.

Al-Warfali said the demonstration continued until 4 a.m. Wednesday, calling it ''an unprecedented state of agitation.''

He also said police arrested another well-known figure, writer Idris al-Mesmari, prompting activists to call for another demonstration in front of the security headquarters.

The protests occurred after several opposition groups in exile called on Monday for Gadhafi's overthrow and for a peaceful transition of power. ''Col. Gadhafi and all his family members should relinquish powers,'' the groups said in a statement. Protesters also called for the ouster of Prime Minister Baghdadi al-Mahmoudi, according to witnesses and videos posted on the Internet. – AP