Dozens of people were killed and injured in the Syrian capital Damascus today when a suicide bomber detonated his explosives belt next to a police bus that had stopped at a traffic light, the state-run Syrian Arab News Agency reported.

It said 25 people were killed and 46 injured. The blast came  just two weeks after a pair of suicide bombings outside government security buildings killed 44.

There was no claim of responsibility for the attack, but the government of President Bashar al-Assad blamed it on terrorists.

State television broadcast grisly images of the aftermath of what it called a "powerful explosion. The pictures included shots of bloodied limbs as well as windows of vehicles and buildings blown out.

A resident told ABC News the site under a bridge is a well-known staging ground for security forces in the Midan District where there have been regular protests since the uprising began in March. The spot is close to several mosques where protests would start, making it easy for the forces to clamp down quickly.

"It appears a suicide bomber blew himself up close to two or three mini buses and one larger one that were carrying police men and other members of the security forces," the Guardian's Ian Black reported from Damascus.

"People are very angry. The scene is pretty grim," he said. "There are pools of blood on the pavement. The remains of the suicide bomber are still there and can be seen. It is pretty terrible sight."

Many opposition activists immediately accused the Assad regime of staging the bombing themselves to justify the accusations of terrorism and armed gangs they have leveled repeatedly.

SANA reported that most of those killed and injured were civilians, though the breakdown was unclear. The security forces are known for deputizing civilians, commonly referred to in Arabic as "shabiha," translated as "thugs."

On Dec. 23, two suicide bombers hit the State Security Directorate and another Security Branch in Damascus. It was the biggest attack in the capital since March.

Until recently, Damascus has been void of the violence seen elsewhere in the country with few outward signs of the conflict.

Today's attack comes as pro-democracy activists and the leader of the opposition Free Syrian Army call on the Arab League to end their observer mission in Syria and admit it failed to stem the violence that the United Nations says has left more than 5,000 people dead.

"We hope they will announce that their mission was a failure," Colonel Riad al As-ad told Agence France-Presse. "We call on the Arab League to step aside and let the United Nations take over responsibility as it is more apt to find solutions."

The Arab League is convening an emergency meeting on Sunday to discuss the situation.