Earlier, activists said fierce fighting in suburbs of the capital Damascus on Tuesday had been the worst there so far.
The UK-based Syrian Observatory for Human Rights said that clashes took place near Republican Guard positions in Qudsiya and al-Hama, about 8km (5 miles) from the centre of Damascus.
Correspondents say it is rare for fighting to take place near Republican Guard bases and suggests a growing confidence among the rebels.
The elite Republican Guard, led by President Assad's younger brother Maher, is tasked with protecting the capital.
Wednesday morning's attack on Ikhbariya TV south of Damascus blew up the newsroom, Sana news agency reported.
"Three journalists and workers" were killed in the attack, it said.
The BBC's Jim Muir in Beirut says the station was targeted by EU sanctions announced on Monday.
Civilians trapped
On Tuesday, Turkey said the rules of engagement for its military had changed after Syria shot down a F-4 Phantom jet over the eastern Mediterranean last week.
Prime Minister Recep Tayyip Erdogan told parliament that if Syrian troops approached Turkey's borders, they would be seen as a threat.
"Every military element approaching Turkey from the Syrian border and representing a security risk and danger will be assessed as a military threat and will be treated as a military target," he said.
Syria insists that the F-4 Phantom was shot down because it was inside Syrian airspace. Turkey says the plane in international airspace.
