An Islamist suicide car bomber reportedly killed at least 50 Syrian security men in Hama province in one of the bloodiest attacks on President Bashar al Assad's forces during a 20-month uprising.

Another day of relentless violence in Syria coincided with more unity talks in Qatar among fractious opposition factions.

State media reported a suicide bomber had targeted a rural development centre in Sahl al Ghab, Hama province, but put the death toll at two.

Rami Abdelrahman, head of the Syrian Observatory for Human Rights, said the centre was used by security forces and pro-Assad militia as one of their local bases.

"A fighter from the Nusra Front blew himself up," he said. "He drove his car to the centre and then blew himself up. A series of explosions followed. At least 50 were killed."

The Nusra Front, an al Qaeda-inspired group of ultra-orthodox Salafi Muslims, has claimed responsibility for several other suicide bombings in Damascus and elsewhere.

The Sana news agency said: "A terrorist blew himself up, which resulted in a number of casualties. Two were killed."

Syrian officials often blame foreign-backed Islamist militants for the revolt, in which about 32,000 people have been killed.

Unity on Syria has also eluded international powers since the conflict began in March 2011, with Russia and China opposing Western calls for his removal.

The conflict has also aggravated divisions in the Islamic world, with Shi'ite Iran supporting Assad and US-allied Sunni nations, such as Saudi Arabia and Qatar backing his foes.