Gunmen have attacked a Syrian pro-government TV channel, killing seven people, state media say. Journalists and security guards died in the attack on Ikhbariya TV south of Damascus, 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. The UN's deputy envoy on Syria says the violence has "reached or surpassed" levels before the April ceasefire deal. As activists put the number of deaths on Tuesday at more than 100, Jean-Marie Guehenno warned the UN Human Rights Council in Geneva that "time was running out". He was speaking shortly before a commission of inquiry gave details of its report on the one of the worst attacks on civilians since the conflict began - the May 25 Houla massacre in which 108 people died. ommission chairman Paulo Pinheiro told the council that "forces loyal to the government may have been responsible for many of the deaths" but he said his team had been unable to determine who was behind the massacre. Mr Pinheiro said the perpetrators were from one of three groups: "shabiha" or other local militia from neighbouring villages, perhaps acting with the army; anti-government armoured groups; or foreign groups. "While the commission could not rule out the possibility of anti-government fighters being responsible for the killing, this was considered very much unlikely," he said. Syrian ambassador Faisal Khabbaz Hamoui condemned the meeting as "flagrantly political" and walked out of the hall. 'Cold blood' The BBC's Jim Muir in Beirut says that 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 20km (14 miles) south of the capital. State TV showed pictures of burnt and wrecked buildings, with fires still smouldering. Syria's Information Minister Omran al-Zoebi, on a visit to the site, said some of the victims had been abducted, bound, and killed in cold blood. He also condemned the EU's decision to impose sanctions on Syria's state-run TV and radio agency for its support of the Assad government. The Ikhbariya attack followed fierce clashes in suburbs of the capital, Damascus, described by opposition activists as the worst there so far. The BBC's Ian Pannell meets a family who are too afraid to take their wounded children to hospital The UK-based Syrian Observatory for Human Rights said fighting had taken place place near positions of the Republican Guard, which is led by President Assad's younger brother Maher and has the role of protecting the capital. 'Seesaw battle' Senior US intelligence officials have described the conflict between the rebels and the government as a "seesaw battle", suggesting that it is 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. Although a general and two colonels were said to have fled to Turkey with 30 other Syrian soldiers earlier this week, the officials said none of the recent defections was key to the government's survival. 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 and the monitors have suspended patrols. Mr Annan hopes to revive the peace plan with an international conference in Geneva on 30 June. Russia has said it will attend the meeting but 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 been killed since pro-democracy protests began in March 2011. In June, the Syrian government reported that 6,947 Syrians had died, including at least 3,211 civilians and 2,566 security forces personnel. The main rebel fighting group, the Free Syrian Army (FSA), has become increasingly better organised - and armed - and is in effective control of swathes of Idlib province and parts of Aleppo province in the north.