DAMASCUS - A suicide bombing hit Damascus on Friday, killing 25 and wounding dozens of mostly civilians, state media said, blaming "terrorists" for the second such attack on the Syrian capital in two weeks.

State television said the "powerful explosion" hit the historic Midan quarter in the heart of the capital.

The Muslim Brotherhood again implicated President Bashar al-Assad's regime in the attack, echoing a charge levelled after the twin suicide blasts last month. "We hold the regime, its agents and its gangs, fully responsible for this crime," the Brotherhood said in a statement received by AFP in Nicosia.

The attack, which took place in a heavily populated neighbourhood near a school, killed 25 people and wounded 45 others, state television said, adding that the casualties were mostly civilians but also some security personnel. It showed gruesome footage of rescuers gathering body parts and placing them in plastic bags, in an area where damaged cars and buses were splattered with blood. Angry residents at the scene shouted and denounced the bombing as the work of "terrorists." The powerful December 23 bombings sparked a swirl of claims and counter-claims over who was responsible, with the authorities saying they were probably the work of Al-Qaeda and the opposition accusing the regime. Such counter-accusations resumed on Friday, with state media labelling the blast a "terrorist bombing" as the Muslim Brotherhood called for an international and Arab probe, saying the attack benefitted the regime. "The killings in Syria will continue and the Syrian regime will keep hiding behind Al-Qaeda and the terrorists... unless someone confronts the regime and takes it to account for its crimes," said the Brotherhood.

"They are the only ones who have the tools and are capable of doing it," said the statement.

The attack came as activists called for an Arab League observer mission to admit its failure to stem nearly 10 months of bloodshed and hand over to the United Nations.

The Arab League mission has been in Syria since December 26 trying to assess whether Assad's regime is complying with a peace accord aimed at ending its deadly crackdown on dissent.

But there has been no let-up in security force fire against civilian demonstrators, with eight people shot dead on Friday, including four in the central city of Hama and three in Damascus province, the Syrian Observatory for Human Right told AFP in Nicosia.

In Homs, a 36-year-old was killed by a security force bullet while sitting on his balcony, the Observatory added.

Protests were also reported in Syria's second city Aleppo and third city Homs, in the port city of Latakia, and in Douma on the northern outskirts of the capital.

Two loud blasts shook the eastern oil hub of Deir Ezzor, where protests were also held, the Observatory said.

And the official SANA news agency reported that a "terrorist group" had blown up an oil pipeline between Hama and Idlib in the northwest.

The Arab League is to meet on Sunday in Cairo to discuss the observer mission, whose credibility continues to be questioned.

"We support the Arab League which has sent observers to Syria but this mission is not at present able to do its job properly," France's Foreign Minister Juppe said on the second day of a visit to Tunisia, without offering further details.

The head of the rebel Free Syrian Army has called on the Arab League to admit the mission's failure and urged the bloc to seek UN help to end the bloodshed.

Colonel Riyadh al-Asaad, in a telephone interview with AFP in Beirut on Thursday, said: "We hope they will announce that their mission was a failure.

"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."

Asaad charged that the government was misleading the monitors and using all means to circumvent the deal it signed with the League, notably by transferring prisoners to areas where the observers cannot visit.

"We, and all the Syrian people, want the United Nations to step in because the Arabs are not capable of taking any real decisions when it comes to Syria," said Asaad.

The UN estimates that more than 5,000 people have been killed in the crisis since March, and the Observatory said regime forces killed another 17 civilians on Thursday alone.

The report came after Qatari Prime Minister Sheikh Hamad bin Jassem al-Thani, who heads an Arab League task force on Syria, admitted "mistakes" in its almost two-week-old mission.

Sheikh Hamad discussed the crackdown with UN leader Ban Ki-moon in New York on Wednesday. A UN spokesman said they held talks on how the UN could assist the Arab League in Syria.

The Local Coordination Committees say at least 390 people have been killed since the observers began their mission.