DAMASCUS: An explosion ripped through a busy intersection in the Syrian capital Friday, hitting a police bus and killing up to 25 people in what Syrian authorities said was the second suicide attack in as many weeks.

The bus was left riddled with shrapnel, blood splattered on its seats and pooled on the asphalt of the street after the blast, which came exactly two weeks after twin bombings targeting intelligence agencies in the capital killed 44 people.

The bombings mark a dramatic escalation of bloodshed as Arab League observers tour the country to investigate President Bashar Assad's bloody crackdown on a 10-month-old popular revolt.

Interior Minister Mohammed Shaar said a suicide bomber ''detonated himself with the aim of killing the largest number of people.''

Syrian television showed residents and paramedics carrying human remains, holding them up for the camera. The explosion damaged a nearby police station, shattering its glass, and left blood and flesh in the streets, according to an Associated Press reporter at the scene. Police cordoned off the area with yellow police tape.

Syria's state media, SANA, said the initial death toll is 25 people. The figure includes 10 people confirmed dead and the remains of an estimated 15 others, whose bodies had yet to be identified. SANA said many of the dead are civilians.

In a sign of just how polarized Syria has become, the opposition has questioned the government's allegations that terrorists are behind the attacks, suggesting the regime itself could have been behind the violence to try to erode support for the uprising and show the observer team that it is a victim in the country's upheaval.

The government has long contended that the turmoil in Syria this year is not an uprising but the work of terrorists and foreign-backed armed gangs.

The opposition has produced no evidence backing its accusations, and no one but Syrian authorities have access to investigate the blasts. A spokesman for the Syrian National Council opposition umbrella group called for an independent probe.

''It is a continuation of the regime's dirty game as it tries to divert attention from massive protests,'' Omar Idilbi said. ''We call upon for an independent international committee to investigate these crimes that we believe that the regime planned and carried out.''

The Arab League observers started work Dec. 27 on a mission to monitor Syria's compliance with a League-drafted peace deal. Under the deal, Assad's regime is supposed to pull its military off the streets of cities and stop its crackdown on the protesters calling for the president's ouster.

Despite the observers' presence, violence has spiked, with Syrian activists saying up to 400 people have been killed since Dec. 21. The UN says the overall toll since the revolt began is more than 5,000.

Friday's blast went off at an intersection in the central Damascus neighborhood of Midan on Friday, the start of the weekend in Syria and much of the Arab world. Midan is one of several Damascus neighborhoods that has seen frequent anti-Assad protests on Fridays since the uprising began in March.

''I heard the explosion at about 11:15 and came running here. I found bodies on the ground including one of a man who was carrying two boxes of yogurt,'' Midan resident Anis Hassan Tinawi, 55, told The Associated Press.

The bus, which was carrying policemen at the time, appeared to be the target of the bomber, said a Syrian official, speaking on condition of anonymity because he was not allowed to speak publicly to the media.

The official also said that a smaller bomb exploded Friday in the Damascus suburb of Tal, killing a girl. Security experts dismantled another bomb in the same area, he said.

Compared to many parts of the country which have been convulsed by the 10-month old uprising, Damascus has been relatively quiet under the tight control of ruthless security agencies loyal to Assad.

But violence in the capital has been on the rise over the last two months. On Dec. 23, according to the Syrian authorities, two car bombers blew themselves up outside the heavily guarded compounds of the country's intelligence agencies, killing at least 44 people and wounding 166.

If the official account is correct, they would be the first suicide bombings during the uprising. State-run TV said the al-Qaida terrorist network was possibly to blame for previous attack, and blamed ''terrorists'' for the latest one, without giving specifics.

Adding to the bloodshed in recent months, dissident soldiers who broke from the military to side with peaceful protesters have launched attacks on government sites, raising fears of civil war.