Seven people have died after gunmen raided the headquarters of a pro-government Syrian TV channel in Damascus, just a few miles from the presidential palace, and set off explosives inside.

State-run Sana news agency reported that an "armed terrorist group" killed seven people during an attack on al-Ikhbaria, a privately owned but pro-Assad satellite channel.

Sana said that the attackers "planted explosive devices in the headquarters of al-Ikhbaria following their ransacking and destroying of the satellite channel studios, including the newsroom studio which was destroyed".

"I heard a small explosion then a huge explosion and gunmen ran in. They ransacked the offices and destroyed the newsroom," an employee who works at the offices in the town of Drousha told state media at the scene.

Pro-regime journalists have been targeted over the country's 16-month uprising.

In retaliation for the attack on the broadcaster, government forces shelled surrounding neighbourhoods and killed at least 33 people.

Information minister Omran al-Zoebi said that the attack was a massacre.

"What happened is a massacre, a massacre against the freedom of the press," Zoebi said. "They carried out a terrifying massacre by executing the employees."

Earlier in June, two Ikhbaria employees were shot and seriously wounded by gunmen in the northwestern town of Haffa.

The assault on the TV station came in the wake of President Bashar al-Assad's admission that his country was "at war".

"We live in a real state of war from all angles," Assad told a cabinet he appointed on Tuesday, in a speech broadcast on state television. "When we are in a war, all policies and all sides and all sectors need to be directed at winning this war."

In other developments, the former leader of Syria's main opposition group, the Syrian National Council, said some areas he visited in north Idilb province were ruling themselves without the presence of the regime.