CAIRO — Libyan protesters celebrated in the streets of Benghazi today, claiming control of the country’s second largest city after bloody fighting, and anti-government unrest spread to the capital with clashes in Tripoli’s main square for the first time. Moammar Gadhafi’s son vowed that his father and security forces would fight “until the last bullet.”

Even as Seif al-Islam Gadhafi spoke on state TV Sunday night, clashes were raging in and around Tripoli’s central Green Square, lasting until dawn today, witnesses said. They reported snipers opening fire on crowds trying to seize the square, and Gadhafi supporters speeding through in vehicles, shooting and running over protesters. Before dawn, protesters took over the offices of two of the multiple state-run satellite news channels, witnesses said.

During the day, a fire was raging at the People’s Hall, the main hall for government gatherings where the country’s equivalent of a parliament holds its sessions several times a year. The pro-government news website Qureyna said flames were seen leaping from the building, and that the headquarters of the Olympics Committee was also on fire.

Protesters were calling for a new protest at sunset today in Green Square, setting up the likelihood of new clashes. Already, armed members of pro-government organizations called “Revolutionary Committees” were circulating in the streets hunting for protesters in Tripoli’s old city, said one protester, named Fathi.

The city was shut down, with schools, government offices and most shops closed except a few bakeries serving residents hunkered down in their houses, said a Tripoli lawyer, Rehab, who like Fathi spoke on condition she be identified only by her first name.

The protests and violence were the heaviest yet in the capital of 2 million people, a sign of how unrest was spreading after six days of demonstrations in eastern cities demanding the end of the elder Gadhafi’s rule.

Gadhafi’s regime has unleashed the bloodiest crackdown of any Arab country against the wave of protests sweeping the region, which toppled the leaders of Egypt and Tunisia. More than 200 have been killed in Libya, according to medical officials, human rights groups and exiled dissidents.

British Prime Minister David Cameron, visiting neighboring Egypt, called the Libyan government’s crackdown “appalling.”

“We can see what is happening in Libya which is completely appalling and unacceptable as the regime is using the most vicious forms of repression against people who want to see that country — which is one of the most closed and one of the most autocratic — make progress. The response they have shown has been quite appalling,” he told reporters in Cairo.