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 President Bashar Assad of Syria 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 the central Damascus neighborhood of Mazzeh al-Jaba, state media said, and activists reported at least 20 rebels were killed in an air raid on the northern town of Harem. The Local Coordinating Committees, made up of activist groups across Syria, said more than 150 people were killed across the country.
On the diplomatic front, the main Syrian opposition bloc broadened its ranks on Monday to accommodate more activists and political groups from inside the country, officials said. The step was an apparent nod to international demands for a more representative and cohesive leadership.
However, the Syrian National Council’s reforms, approved on the second day of a five-day summit in Doha, Qatar, may not be enough to counter a US-backed plan to create a new opposition leadership that would greatly dilute the National Council’s influence.
The United States has criticized the council, which was dominated by exiles and academics, as ineffective and out of touch with those fighting in Syria to overthrow Assad. Under the US-backed plan, proposed by prominent dissident Riad Seif, the council would become part of a new leadership group, holding only 15 of the organization’s 50 seats — thus making room for more representatives from inside Syria.
Monday’s fighting in Damascus was some of the worst since July, when rebels took over several neighborhoods of the capital, 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 front in the civil war since then.
The attacks on the two main cities have demonstrated new organization and capabilities of rebel forces as well as a determination to press their uprising despite the deaths of more than 36,000 people 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 the 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 Assad. The fighting in the Damascus-area Palestinian refugee camp of Yarmouk started Sunday when residents were attacked by gangs who said they include Palestinians fighting the government.
Video of the Yarmouk fighting that was 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, which continued Monday. The Observatory said the fighting in Damascus was concentrated in the outskirts of the camp and the southern neighborhood of Tadamon.
‘‘Tadamon is being struck with shells, rockets, and heavy machine-gun fire,’’ activist Abu Qais al-Shami said. ‘‘People are fleeing the area toward safer areas inside the Yarmouk camp.’’
A Syrian opposition figure, who asked not to be identified out of fear of reprisal, said Palestinian fighters who are opposed to Assad were fighting alongside the rebels in Damascus.
In northern Syria, an opposition figure said rival rebel groups clashed Sunday for control of the Bab al-Salameh border crossing with Turkey. The crossing has been in the hands of rebels since July. The opposition figure spoke on condition of anonymity because of fear of retaliation.