An Islamist militant group has claimed responsibility for the kidnap and killing of a Syrian television presenter and has threatened more attacks on supporters of President Bashar al-Assad, the SITE monitoring group which tracks Jihadist websites said on Sunday.

The Syrian Observatory for Human Rights had said that Syrian state television presenter Mohammed al-Saeed, who was kidnapped from his home in mid-July, had been executed.

SITE said the Al Nusra Front stated in one of four communiques posted on Islamist forums on August 3 that it had kidnapped Saeed in Damascus province on July 19, and killed him after subjecting him to interrogation.

"Perhaps this operation and others will serve as an example to all who support this tyrannical regime, so that they may repent to God," SITE quoted the militant group as saying in a statement. "Otherwise, the swords of the mujahideen will cut off their heads and purify the Levant (Syria) from their obscenity."

It was not immediately possible to verify the claim from the group, which was unknown before it claimed responsibility for a series of bombings in Damascus and Aleppo that started in December.

Last month, the group claimed responsibility for a raid and bombing on June 27 of Ikhbariya headquarters, a pro-government Syrian TV channel, in which seven people were killed.

In June, the Al Nusra Front claimed responsibility for the killing of 13 men whose bodies were found bound and shot in the city of Deir al-Zor in eastern Syria on May 29. The killings condemned by United Nations monitors as "appalling and inexcusable".

Camille Tawil, a historian of Islamist armed groups and writer for the pan-Arab al-Hayat newspaper has said the group was alienating the majority of the Syrian opposition.

SITE quoted Al Nusra Front as saying in another communique that its fighters, in a joint operation with the Al Sahaba Battalion - part of the Free Syrian Army, stormed a police station in Jdeidet Artouz, near Damascus, destroying it and capturing equipment and weaponry.