An explosion outside a mosque in Syria's capital killed five security personnel on Friday and wounded several others, state television said.

Syria TV said the "terrorist" blast had been caused by explosives attached to a motorcycle in the Damascus neighborhood of Rukn al-Din.

The 17-month-old revolt against President Bashar al-Assad's rule has grown increasingly bloody in recent months, as rebels try to bring the fight to his seat of power in Damascus and to the economic hub, Aleppo.

Assad's forces have cracked down with troops, tanks and helicopter gunships on the unrest, which began as a series of peaceful protests but has now descended into civil war.

An opposition group, the Syrian Observatory for Human Rights, said Friday's blast had been aimed at a security patrol in the area.

The British-based group, which has a network of activists across Syria, said that, in addition to the five dead, the explosion had wounded six members of the security forces, leaving several in critical condition.