A suicide bombing in the Syrian capital of Damascus has killed nine and wounded 20, according to state TV.

The attack, which occurred in the Midan area of the city, was the second to strike the capital on Friday and the latest in a string of bombings in Syrian cities in recent months.

Elsewhere, United Nations Secretary General Ban Ki-moon said he was gravely alarmed with Syrian president Bashar al-Assad's refusal to withdraw troops from urban areas as part of a six-point peace plan proposed by UN/Arab League envoy Kofi Annan and ostensibly agreed to by Syrian officials.

In a written report, the UN chief said he was: gravely alarmed by reports of continued violence and killing.

Friday's attack occurred just over the road from a mosque, the usual gathering point for protests which usually take place across the country on Fridays.

Earlier in the day a separate blast occurred in an industrial part of the city, but it was not clear if there were any casualties, according to CNN.

Friday's blasts followed a massive explosion in the Syrian city of Hama on Thursday which killed 70 people, according to opposition forces.

Rebels claimed the blasts were caused by intense shelling, however, state media organization SANA said armed terrorist groups had accidentally detonated a bomb that leveled nearby buildings.

At least 462 people have been killed since the UN's mission started on April 16, according to the opposition Local Coordination Committees of Syria, with over 9000 killed so far during the 13-month-old-conflict according to UN estimates.