Police spokesman Ranjith Gunasekara said authorities did not know who the attackers were or what their motive may have been, but promised a full investigation.

However, rights activists said the assault may have stemmed from recent accusations that the Maharaja Organisation and its three television stations and four radio channels have not given sufficient coverage to the government's victories over ethnic Tamil rebels.

More than a dozen heavily armed intruders overwhelmed the security guards outside the company's studio and transmission compound near the capital, Colombo, at about 2 am, badly beating one man and holding the others at gunpoint, several guards said.

The attackers ordered a guard to bring them to the main control room, where they shot out television screens, glass doors and editing equipment, the guards said, refusing to give their names because of fear of reprisals.

Several employees were assaulted, but no one was hospitalised, said Susil Kindelpitiya, news director of Sirasa TV, one of Maharaja's channels. The attack caused extensive damage to the network's broadcasting facilities, he said.

Throughout the morning, the television stations broadcast live reports from the building, showing footage of burnt equipment and other destruction.

Kindelpitiya said he believed the attack was due to 'our unbiased reporting,' but did not say who he thought the culprits were.

Poddala Jayantha of the Working Journalists Association, a media rights group said the government created the atmosphere that led to the violence.

Some lawmakers were recently quoted in the state media accusing the Maharaja group of failing to publicize the successes of government forces over Tamil separatists in the ongoing civil war.

Government troops seized the Tamil rebel administrative capital of Kilinochchi on Friday in one of the military's greatest victories over the insurgents.

Sri Lankan media, including Maharaja, gave the event wide coverage, but nationalist politicians have in the past accused the station of sympathizing with the rebels.

On Saturday, several gasoline bombs were hurled at the station, but police did not take steps to protect it, said Jayantha. Guards told police that a vehicle without a license plate appeared to be casing the compound, the station reported on its newscast.

Media watchdog groups say intimidation of journalists has grown as the civil war between government forces and Tamil Tiger rebels escalated over the past two years.

In November, Amnesty International said Sri Lankan journalists face arbitrary detentions and attacks, with at least 10 media employees killed since 2006 and one missing since being arrested two years ago.

The government has denied it is behind attacks and has appointed a committee of ministers to investigate complaints. -- AP