The Tripoli headquarters of Libya's Alassema privately owned television channel was attacked early Wednesday, with three powerful blasts heard, an AFP journalist said.

A source at the broadcaster said three rocket-propelled grenades were fired at the building, and that a guard was lightly wounded.

The journalist also heard gunfire in the area for several minutes shortly after midnight before the explosions rocked the complex in the Gurji district near central Tripoli.

Transmission of programmes was not affected.

Alassema is known for its anti-Islamist stance, and was also attacked nearly a year ago, last March.

Gunmen attacked the station, ransacked offices and took away the owner and several presenters before freeing them several hours later.

The channel has been accused by Islamists of urging people to demonstrate against the country's highest political body, the General National Congress.

The GNC on February 3 took the controversial decision to extend its mandate until December, despite opposition by much of the population critical of its inability to halt Libya's slide into chaos.

A week ago, the headquarters of two private television channels in the restive eastern city of Benghazi were targeted by gunmen.

It was in Benghazi, Libya's second city, that the uprising against dictator Moamer Kadhafi first erupted in February, 2011.

Benghazi has seen several kidnappings and murders of journalists.

In December, gunmen abducted and killed the owner-director of one Tripoli radio station in still unexplained circumstances.

Media watchdog Reports Without Borders has repeatedly warned of the threat to journalists posed by former rebel militias that helped topple the Kadhafi regime.

It said the threat was greatest in Benghazi, but also existed in Tripoli and elsewhere.

On Tuesday, gunmen released a reporter for Libya's state media a day after kidnapping him in the capital.

Since Kadhafi's death, the government has struggled to restore order and the media has come under mounting threat from former rebels.