Syrian television reports that a bomb has exploded on the third floor of the state TV and radio building in the capital, Damascus.
Three people were reported wounded and the explosion caused some damage but state TV continued broadcasting.
Rebel forces took over several areas of Damascus in recent weeks, but the army has since regained control of the city.
More than 20,000 troops are now aiming to wrest control of the country’s second city, Aleppo, from the rebels.
A bomb has exploded on the third floor of Syrian state TV and radio building in the capital, Damascus
The explosion in Umawiyeen Square in central Damascus had “ripped the floor” but had left the transmission of the three Syrian channels unaffected.
Pro-government TV channel al-Ikhbariya showed pictures of staff looking after an injured colleague. In June, gunmen attacked its offices, south of Damascus, killing seven people, including journalists and security guards.
Information Minister Omran al-Zoabi told Syrian TV that national media had been targeted in the “desperate and cowardly” attack. An investigation was under way to find out who planted the bomb inside the building, he added.
State TV’s buildings have also been attacked in many provincial cities, most recently in Aleppo.
The army has surrounded Aleppo, Syria’s commercial capital, and tanks have tried to push into two key rebel-held areas, Salah al-Din and Saif al-Dawla, which lie on the main road into the city.
A rebel commander was one of nine people killed in Salah al-Din on Monday, according to British-based group the Syrian Observatory for Human Rights.
Gunmen have attacked Ikhbariya TV, a Syrian pro-government TV channel, killing three people, state media say.
The attack on Ikhbariya TV south of Damascus blew up the newsroom, Sana news agency reported.
Hours earlier, President Bashar al-Assad said Syria was in “a real state of war” and US intelligence officials predicted a long, drawn-out struggle.
UN human rights investigators, in their latest report, say the conflict is descending into civil war.
Syrian TV dropped normal programming on Wednesday to run live coverage of the attack on the headquarters of Ikhbariya TV in the town of Drusha, some 20 km (14 miles) south of the capital.
State TV showed pictures of burnt and wrecked buildings, with fires still smouldering.
Syria’s information minister, on a visit to the site, said the three victims had been abducted, bound, and killed in cold blood.
Gunmen have attacked Ikhbariya TV, a Syrian pro-government TV channel, killing three people
On Monday, the station was targeted by EU sanctions.
The attack comes after fierce clashes in suburbs of the capital Damascus described by opposition activists as the worst there so far. Dozens of people were killed.
The UK-based Syrian Observatory for Human Rights said fighting took place near positions of the Republican Guard which is led by President Bashar al- Assad’s younger brother Maher and has the role of protecting the capital.
In a separate development, Syrian sources said that a senior air force officer, Maj-Gen Faraj Shehadeh, was abducted by armed men from his home in Damascus.
The latest violence gives added point to Bashar al- Assad’s description of Syria as in “a state or war” just a few hours before.
Addressing his new cabinet, the president criticized countries that have been calling for him to stand down, saying that the West “takes and never gives and this has been proven at every stage”.
Senior US intelligence officials have described the conflict between the rebels and the government as a “seesaw battle”, suggesting that it likely to be a long drawn-out, struggle.
“The regime inner circle and those at the next level still seem to be holding fairly firm in support of the regime and Assad,” one official was quoted by Reuters as saying during a briefing to reporters.
Recent defections were described as low or mid-level.
Earlier this week, a general and two colonels were said to have fled to Turkey with 30 other Syrian soldiers.
Human rights investigators have released their latest report on Syria, including their findings on the Houla massacre.
A commission of inquiry, which has been investigating human rights violations for the UN Human Rights Council, says that what began as government suppression of peaceful demonstrators has turned, in many areas, into civil war.
The Geneva-based UN council called on the commission earlier this month to find out who carried out last month’s killings in Houla in which 108 people died.
In April, following months of bloodshed, the Syrian government agreed to a six-point peace plan brokered by UN-Arab League envoy Kofi Annan. UN monitors were deployed to Syria to oversee a ceasefire but the truce never took hold.
On Tuesday Russia said its Foreign Minister, Sergei Lavrov, would attend an international conference on Syria which Kofi Annan hopes to hold in Geneva on 30 June to revive his peace plan.
However, Moscow is insisting that Iran also be allowed to attend, a move strongly opposed by the US and its allies.
The UN says at least 10,000 people have died in the uprising that began in March 2011. The Syrian government says 6,143 Syrian citizens have been killed by “terrorist groups” since.
The main rebel fighting group, the Free Syrian Army (FSA), has become increasingly better organized – and armed – and is in effective control of swathes of Idlib province and parts of Aleppo province in the north.