Syrian state media say a suicide bombing has rocked central Damascus, killing and wounding dozens of people.

The official SANA news agency is reporting that the attacker blew himself up on Friday at an intersection in the capital's central district of Midan. It said most of the causalities are civilians, but includes some security personnel.

Media reports say a bus carrying policemen appeared to the be target of the attack.

Television footage shows shattered windows and blood splattered on what appears to a police bus. The footage also shows riot gear inside the bus that is surrounded by damaged vehicles, and people shouting that it was the work of terrorists.

No one has claimed responsibility for the attack, which comes two weeks after twin blasts targeting security buildings in Damascus killed 44 people.

Meanwhile, there is mounting criticism over the effectiveness of an Arab League mission in Syria that is monitoring President Bashar al-Assad's compliance with a plan to end a bloody, 10-month crackdown on protesters.

Syrian activists are calling for huge protests Friday in support of international assistance, a day after Qatar's prime minister conceded that the Arab League observer mission has made “mistakes.”

Qatar's Sheikh Hamad bin Jassim al-Thani said on Thursday that United Nations assistance is needed to improve the monitoring of Mr. Assad's government. He chairs the Arab League committee on Syria.

The Arab League will meet in Egypt on Sunday to assess the mission's initial findings in Syria and to decide whether it will continue. The initial 50 observers arrived on December 26 to monitor the Syrian government's compliance with a plan to end the violence.

The Arab League effort is aimed at ensuring Mr. Assad follows through on his pledge to withdraw security forces from cities, release political prisoners and allow anti-government demonstrations.

The United Nations estimates that 5,000 have died since the uprising began in March. In comparison, global activist group Avaaz says it has verified through multiple independent sources that nearly 7,000 people have been killed in the Syrian unrest.

Syria's main opposition leader, Burhan Ghalioun, is also calling for international assistance in Syria. He said in interviews with British media on Thursday that Western countries should establish a no-fly zone over parts of the country. Ghalioun emphasized it could be on a smaller scale than the NATO-led no-fly zone in Libya, but said it could help support the revolution.

The leader of the Syrian National Council told the BBC and The Telegraph that the Arab League needs to prove that it is seriously challenging Mr. Assad's government.