Gunmen killed four people in three attacks on Sunday in the northern Iraqi city of Mosul, officials said.

Violence has dropped in Iraq since the country's worst sectarian fighting in 2006 and 2007, but insurgents carry out near-daily attacks on security forces and civilians to try to undermine the Shiite-led government.

Assailants fired at a police checkpoint in the center of Mosul, killing two policemen, police said. Later in the day, gunmen killed an off-duty soldier at a car repair shop in the city. In a third attack, gunmen fired at a van carrying oil workers, killing one and wounding three, police said.

A health official confirmed the casualty figures.

The health official and two police officers spoke anonymously because they were not authorized to publicly release the information.

Also on Sunday, the head of the Nalia satellite TV station in Iraq's autonomous Kurdish region confirmed that a bomb exploded on the roof of the station, causing no casualties.

The bomb went off on Saturday, a day after a caller to the station's call-in program was perceived to be insulting the father of Massoud Barzani, the president of the autonomous region, station chief Sarwa Abdul-Wahid said.

A day after the call, several hundred Barzani supporters demonstrated outside the station and tried to break in, but were stopped by police, Abdul-Wahid said. Later that day, the bomb exploded on the roof.