CAIRO (AP) -- Libyan protesters celebrated in the streets of Benghazi on Monday, 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."

Protesters demanding Gadhafi's ouster planed new marches in the capital's main Green Square and at the leader's residence for Monday evening. That was likely to bring a new round of violence after a similar march the night before prompted clashes that lasted till dawn, with witnesses reporting snipers opening fire on protesters and Gadhafi supporters racing through crowds in trucks and cars, firing automatic weapons and running people over.

During the day Monday, 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 web site Qureyna said. It also reported the first major sign of discontent in Gadhafi's government, saying justice minister Mustafa Abdel-Jalil resigned from his post to protest the "excessive use of force against unarmed protesters."

The capital was largely shut down, with schools, government offices and most stores closed, as armed members of pro-government organizations called "Revolutionary Committees" circulated in the streets hunting for protesters in Tripoli's old city, said one protester, named Fathi.

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 son, Seif al-Islam, went on state TV late Sunday night, warning civil war will break out if protests continue, a theme continued Monday on Libyan state TV, where a pro-regime commentator spoke of chaos and "rivers of blood" turning Libya into "another Somalia" if security is not restored.

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.

Fragmentation is a real danger in Libya, a country of deep tribal divisions and a historic rivalry between Tripoli and Benghazi. The Arab world's longest ruling leader in power for nearly 42 years, Moammar Gadhafi has held an unquestioned grip over the highly decentralized system of government he created, called the "Jamahiriya," or "rule by masses."

Libya's former ambassador to the Arab League in Cairo, Abdel-Moneim al-Houni, who a day earlier resigned from his post to side with protesters, issued a statement demanding Gadhafi "be put on trial along with his aides, security and military commanders over the mass killings in Libya."

"Gadhafi's regime is now in the trash of history because he betrayed his nation and his people," al-Houni said.

The spiraling turmoil in Libya, an OPEC country that is a significant oil supplier to Europe, was raising international alarm. Oil prices jumped $1.67 to nearly $88 a barrel Monday amid investor concern.

Two leading oil companies, Statoil and BP, said they were pulling some employees out of Libya or preparing to do so. Portugal sent plane to pick up its citizens and other EU nationals and Turkey sent two ferries to pick up construction workers stranded in the unrest-hit country. EU foreign ministers were discussing on Monday the possible evacuation of European citizens. Mobs attacked South Korean, Turkish and Serbian construction workers at various sites around the country, officials from each country said.

The Internet has been largely shut down in Libya, residents can no longer make international calls from land lines and journalists cannot work freely, but eyewitness reports trickling out of the country suggested that protesters were fighting back more forcefully. Most witnesses and residents spoke on condition they be indentified by first name only or not at all, out of fear of retaliation.

In Libya's second largest city, Benghazi, protesters were in control of the streets Monday and took over the main security headquarters, known as the Katiba, after bloody clashes Sunday that killed at least 60 people, according to a doctor at the main hospital.

Cars honked their horns in celebration and protesters in the streets chanted "Long live Libya." Protesters took down the Libyan flag from above Benghazi's main courthouse and raised the flag of the country's old monarchy, which was toppled in 1969 by the military coup that brought Moammar Gadhafi to power, according to witnesses and video footage posted on the Internet.

Benghazi's airport was closed, according to an airport official in Cairo. A Turkish Airlines flight trying to land in Benghazi to evacuate Turkish citizens Monday was turned away, told by ground control to circle over the airport then to return to Istanbul.

There were fears of chaos as young men - including regime supporters - seized weapons from the Katiba and other captured security buildings. "The youths now have arms and that's worrying," said Iman, a doctor at the main hospital. "We are appealing to the wise men of every neighborhood to rein in the youths."

Youth volunteers were directing traffic and guarding homes and public facilities, said Najla, a lawyer and university lecturer in Benghazi. She and other residents said police had disappeared from the streets.

Benghazi has seen a cycle of bloody clashes over the past week, as security forces kill protesters, followed by funerals that turn into new protests, sparking new bloody shootings. After funerals Sunday, protesters fanned out, burning government buildings and police stations and besieging the Katiba.

Security forces battled back, at times using heavy-caliber machine guns and anti-aircraft guns, according to residents. One witness said she saw bodies torn apart and that makeshift clinics were set up in the streets to treat the wounded. Ahmed Hassan, a doctor at the main Al-Jalaa hospital, said funerals were expected Monday for 20 of those killed the day before, but that families of 40 others were still trying to identify their loved ones because their bodies were too damaged.

In some cases, army units reportedly sided with protesters against security forces and pro-Gadhafi militias. Mohamed Abdul-Rahman, a 42-year-old Benghazi merchant, said he saw an army battalion chasing militiamen from a security compound.

After seizing the Katiba, protesters found the bodies of 13 uniformed security officers inside who had been handcuffed and shot in the head, then set on fire, said Hassan, the doctor. He said protesters believed the 13 had been executed by fellow security forces for refusing to attack protesters.

Protest leaders and army units that sided with them were working to keep order in the streets Monday, directing traffic and guarding homes and official buildings, several residents said.

On Sunday night, Gadhafi's son Seif el-Islam - long seen as his likely successor - took to state TV, trying to take a tough line in a rambling and sometimes confused speech of nearly 40 minutes.

"We are not Tunisia and Egypt," he said. "Moammar Gadhafi, our leader, is leading the battle in Tripoli, and we are with him."

"The armed forces are with him. Tens of thousands are heading here to be with him. We will fight until the last man, the last woman, the last bullet," he said.

He warned the protesters that they risked igniting a civil war in which Libya's oil wealth "will be burned." He also promised "historic" reforms in Libya if protests stop.

Seif has often been put forward as the regime's face of reform. Several of the elder Gadhafi's sons have powerful positions in the regime and in past years have competed for influence. Seif's younger brother Mutassim is the national security adviser, with a strong role in the military and security forces, and another brother Khamis heads the army's 32nd Brigade, which according to U.S. diplomats is the best trained and best equipped force in the military.

Even as Seif spoke, major clashes had broken out for the first time in Tripoli.

Sunday afternoon, protesters from various parts of the city began to stream toward central Green Square, chanting "God is great," said one 28-year-old man who was among the marchers.

In the square, they found groups of Gadhafi supporters, but the larger number of protesters appeared to be taking over the square and surrounding streets, he and two other witnesses said. That was when the backlash began, with snipers firing down from rooftops and militiamen attacking the crowds, shooting and chasing people down side streets. they said.

Gadhafi supporters in pickup trucks and cars raced through the suqare, shooting automatic weapons. "They were driving like mad men searching for someone to kill. ... It was total chaos, shooting and shouting," said the 28-year-old.

The witnesses reported seeing casualties, but the number could not be confirmed. One witness, named Fathi, said he saw at least two he believed were dead and many more wounded.

After midnight, protesters took over the main Tripoli offices of two state-run satellite stations, Al-Jamahiriya-1 and Al-Shebabiya, one witness said.