An attack on a pro-government television channel's offices near Damascus killed three staff on Wednesday after President Bashar al-Assad said Syria was in a "state of war."

As the UN Human Rights Council prepared to hear a new report by a panel it set up to probe the conflict, human rights monitors said that 79 civilians were among at least 129 people killed in violence on Tuesday.

Live footage broadcast by state television showed extensive damage to the studios of the Al-Ikhbariya satellite channel with several small fires still burning in what it described as an unprecedented attack on the pro-government media.

"The terrorist groups stormed the offices of Al-Ikhbariya, planted explosives in the studios and blew up them with up along with the equipment," Information Minister Omran al-Zohbi told the television in a live interview.

"They carried out the worst massacre against the media, executing journalists and security staff," Zohbi said.

"This didn't come out of nowhere," he added, pointing to European Union sanctions imposed on the pro-government media.

An unidentified pro-government television channel was among the organisations hit by the latest round of EU sanctions against the Syrian authorities imposed on Monday.

Washington put the state broadcaster on its sanctions blacklist in March.

Al-Ikhbariya remained on the air despite Wednesday's assault.

With the uprising now in its 16th month, Assad told his cabinet Tuesday that Syria was in a "real situation of war" and ordered ministers to crush the anti-regime revolt even as fierce fighting broke out near the capital Damascus.

"When one is in a state of war, all our policies and capabilities must be used to secure victory," he said, according to the official SANA news agency.

Fighting broke out in the suburbs of Damascus on Tuesday between rebel forces and Syrian army units, around elite Republican Guard posts, the London-based Syrian Observatory for Human Rights said.

It was the first time that artillery had been used "so close to the capital", Observatory head Rami Abdel Rahman told AFP in Beirut.

SANA reported that government forces had clashed with "armed terrorist groups" in the suburb of Al-Hama, killing dozens and arresting others.

Turkish Prime Minister Recep Tayyip Erdogan meanwhile moved to denounce Syria's downing last Friday of a Turkish Phantom F-4 fighter jet in far more aggressive terms than his initial, cautious statements over the weekend.

"This is a hostile act... a heinous attack," Erdogan said, adding that the military's standing orders had been adjusted accordingly.

"The rules of engagement of the Turkish Armed Forces have changed given this new development," he said.

Damascus has defended the downing of the jet, saying it was a response to "a gross violation" of its sovereignty as the aircraft had entered Syrian airspace.

But NATO condemned the action after a meeting called by Turkey, an alliance member.

"It is another example of the Syrian authorities' disregard for international norms, peace and security, and human life," NATO chief Anders Fogh Rasmussen said. The jet's two pilots are still missing.

Russia appealed for calm.

"We believe it is important that the incident is not viewed as a provocation or an intentional action, and that it does not lead to destabilising the situation," a foreign ministry statement said.

Washington rejected a Russian proposal for Iran to take part in a planned international conference on Syria in Geneva on Saturday.

"It is better to involve Iran in the settlement (of the Syrian crisis)," Russian President Vladimir Putin told reporters in Jordan. "In any case it would complicate the process (if Iran is ignored)."

State Department spokeswoman Victoria Nuland told reporters in Washington however that the US did not think Iran could make a useful contribution given its support for the Damascus regime.

State Department officials have also said that Secretary of State Hillary Clinton will not attend the meeting unless all parties first agree on the need for political change in Syria.

A senior official travelling with Clinton said the Geneva conference was threatened by Russia's refusal to consider Assad's departure, but that a deal might yet be done.

"The sticking point is a clear agreement that there needs to be a political transition," the official said late Tuesday.

The UN Human Rights Council was meanwhile to hear a new report from the Independent Commission of Inquiry on Syria, its first since the panel's president, Paolo Sergio Pinheiro, was allowed into Syria for the first time since the inquiry was set up last August.

The latest report was to include the panel's findings on the deaths of scores of civilians, most of them women or children, in an artillery bombardment and militia assault on the central town of Houla last month.