BEIRUT // A little-known militant group says it carried out a double-suicide bombing in Damascus on Thursday that killed 55 people and injured hundreds.
In an online video, Al Nusra Front says the attack "fulfilled our promise to respond" to the brutal suppression of protesters by the regime of Syria's president, Bashar Al Assad.
The declaration is the latest sign that Syria's 14-month-old uprising could be veering towards civil war.
"We promised the regime in our last declaration to respond to its killing of families, women, children and old men in a number of Syrian provinces, and here we kept our promise," says a garbled voice to a background of Islamist chants.
Al Nusra Front has claimed responsibility for several other recent attacks, including another twin bombing in the capital this month that killed 20 security personnel, according to a report on Thursday by the US-based SITE Monitoring Service, which tracks terrorism incidents.
Intelligence officials believe it could be another sign that radical Islamists have gained influence in battles between government forces, defecting soldiers and other regime opponents.
They say Al Nusra could be a front for an Al Qaeda branch operating in Iraq.
Security fficials in Iraq have observed a number of terrorism suspects - including those with explosives expertise - moving to Syria to battle government forces recently.
At least 9,000 people have been killed since Syria's unrest began in March 2011, according to the United Nations, and as many as 12,000 according to the British-based Syrian Observatory for Human Rights. Hundreds have been killed by government forces since an April 12 ceasefire agreement between the government and opposition groups that was brokered by the joint Arab League-UN envoy, Kofi Annan.
Yesterday, the Observatory said government forces killed at least three people during attacks in the provinces of Hama, Homs and Idlib.
At least a dozen more were killed a day earlier, including an 11-year-old child struck by sniper fire in the city of Deraa, as tens of thousands of people demonstrated after Friday prayers, the organisation said.
Syrian state television said on Friday the army had foiled an attempted suicide attack in the city of Aleppo. The bomber carried 1,200 kilograms of explosives in his car, it said.
"The Syrian authorities have foiled an attempted suicide attack in Al Shaar area in Aleppo, and killed the would-be attacker," it said.
The Thursday bombings in Damascus were the largest suicide attacks ever in the capital, shearing off the face of a nine-storey building used by military intelligence.
The attack's alleged plotters in Al Nusra Front directed their ire at both the government of Mr Al Assad and the religion of his family.
"We tell this regime: stop your massacres against the Sunni people. If not, you will bear the sin of the Alawites," a voice says in the video. The Alawites are the minority religious sect, an offshoot of Shiite Islam, of the ruling Al Assad family.
Syria's state-run media have accused Qatar and Saudi Arabia of playing a role in the attack.
* With additional reporting from the Associated Press and Agence France-Presse