(AP) BEIRUT - A video posted online in the name of a shadowy militant group late Friday claimed responsibility for twin suicide bombings in the Syrian capital this week that killed 55 people.
In the video, a group calling itself the Al-Nusra Front says the bombing was in response to attacks on residential areas by the regime of President Bashar Assad.
"We fulfilled our promise to respond with strikes and explosions," a distorted voice says, reading black text that rolls across a white screen while Islamic chanting plays in the background.
The Al-Nusra Front has claimed past attacks through statements posted on militant websites. Little is known about the group, although Western intelligence officials say it could be a front for an al Qaeda branch operating in Iraq. The video's authenticity could not be independently verified.
Western officials say there is little doubt that Islamist extremists, some associated with al Qaeda, have made inroads in Syria as instability has spread since the start of the uprising against President Bashar Assad 14 months ago.
But much remains unclear about their numbers, influence and activities inside Syria.
Their presence adds a wild card element to the Syria conflict that could further hamper international efforts to end it.
World powers are backing a peace plan presented by international envoy Kofi Annan that calls for a cease-fire to allow for talks on a political solution to the conflict.
A shipment of supplies for U.N. observers monitoring the truce arrived in Damascus Sunday. It included six armored cars, the first of 25 to arrive Saturday for use by the 105 military observers and 45 support staff currently in the country.
But while foreign diplomats and observers can pressure the government and the opposition to stick the plan, they have no means of influencing shadowy Islamic militants.
Friday's video said the Damascus attack was in response to Syrian government attacks on residential areas.
"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," it says.