BEIRUT -- New chaos engulfed Syria's civil war Monday as Palestinian supporters and opponents of the embattled regime were swept up in intense fighting in Damascus, while rival rebel groups clashed over control of a Turkish border crossing.
The rare infighting -- accompanied by car bombs, airstrikes and artillery shells that killed or maimed dozens of people -- heightened fears that if Syrian President Bashar Assad falls, the disparate factions battling the regime will turn on each other.
A suicide bomber detonated his explosives-laden car near an army checkpoint in Hama province, killing 50 soldiers in one of the deadliest single attacks targeting pro-Assad troops in the 19-month uprising, according to activists. Eleven civilians died when a bomb exploded in a central Damascus neighborhood, state media said, and activists reported at least 20 rebels killed in air raid on the northern town of Harem.
"It's the worst-case scenario many feared in Syria," said Fawaz Gerges, director of the London School of Economics' Middle East Center. "It's an all-out war."
Fighting in Damascus, the capital, was some of the worst since July, when rebels seized several neighborhoods, only to be bombed out by regime forces days later. Shortly after those battles, rebels moved on Syria's largest city, Aleppo, and it has become a major civil war front since then.
The attacks on the two main cities have demonstrated rebel forces' new organization and capabilities as well as a determination to press their uprising despite deaths of more than 36,000 in almost 20 months of fighting.
When Syria's unrest began in March 2011, the country's half-million Palestinians struggled to stay on the sidelines. But in recent months, many Palestinians started supporting the uprising, although they insisted that opposition to the regime should be peaceful. One faction, the Popular Front for the Liberation of Palestine-General Command, led by Ahmed Jibril, has remained loyal to Mr. Assad.
The popular committees in the Damascus-area Palestinian refugee camp of Yarmouk, which are led by the PFLP-GC, said the fighting started Sunday when residents were attacked by gangs who claimed to include Palestinians fighting the government.
"The mercenaries who claim to have Palestinians among them" tried to infiltrate the camp, but were repulsed by the popular committees, the statement said Monday. It added that when the rebel attack failed, they fired mortars that killed or wounded several people.
Video of the Yarmouk fighting posted online by activists Monday showed destruction around the camp, with shell-pocked and scorched vehicles, and shattered windows in apartment buildings, as residents picked through debris and shouted in disbelief. The video was consistent with Associated Press reporting on the fighting in the area.
Rami Abdul-Rahman, who heads the Britain-based activist group Syrian Observatory for Human Rights, had no word on casualties from fighting that continued Monday. He said eight people were killed in Yarmouk on Sunday night when several mortar rounds landed in the camp.
"Those who are shelling the camp are terrorists" seeking to displace the Palestinians again, PFLP-GC spokesman Anwar Raja told the AP in Damascus.
Syrian authorities blame the uprising on a foreign plot, accusing Gulf nations Saudi Arabia and Qatar -- along with the United States, other Western nations and Turkey -- of funding and training the rebels, whom they describe as "terrorists."