Armed men attacked a private Sri Lankan television station early Tuesday, tossing hand grenades, spraying the building with gunfire and sparking a blaze that caused heavy damage, witnesses and police said.

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

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

• Click here for photos.

The attack was the latest in a string of recent assaults against journalists. Some reporters have sought asylum abroad, while others have resorted to self-censorship to deflect accusations they are unpatriotic.

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 a.m., 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 hospitalized, said Susil Kindelpitiya, news director of Sirasa TV, one of Maharaja's channels.

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

Media Minister Anura Yapa said the government condemned the attack, adding that President Mahinda Rajapaksa called on police to conduct a thorough investigation.

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.

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.