Four suicide bombers entered the headquarters of the Salaheddin television channel in Tikrit, north of Baghdad, a police lieutenant colonel said. There were three explosions inside, the cause of which was unknown.

A police major said militants set off a car bomb at the gate of the building, after which a suicide bomber detonated explosives and militants moved in.

According to reports, security forces had surrounded the building and were waiting to move in.

The number of casualties was not immediately clear, but some people were still trapped inside the building, journalists said.

"I managed to escape, and I am outside the building, and the third and the fourth floors are on fire now," a Salaheddin journalist told AFP by telephone.

"Some of my colleagues are trapped in the building, among them two women. I am calling them on their mobile phones and they are not answering," he said.

A journalist from Iraqiya state TV, which has an office in the same building, said he was among those who were able to escape, while others were still trapped inside.

Seven Iraqi journalists have been killed in attacks in less than three months.

Violence in the country has reached a level not seen since 2008.

More than 6,650 people have been killed in Iraq since the beginning of the year, according to AFP figures based on security and medical sources.

NJF/NJF