Gunmen Friday shot dead 18 people -- most of them Iranians -- who were working on a gas pipeline from Iran to Iraq northeast of Baghdad, police officers said.

The attack near Baladruz killed 15 Iranians and three Iraqis, and wounded five Iranians and two Iraqis, the officers said.

Violence has reached a level this year not seen since 2008, when Iraq was just emerging from a period of brutal sectarian killings.

The surge in unrest has raised fears the country is falling back into all-out conflict.

It took just eight days for this month's death toll to surpass that for the entire month of December last year, according to AFP figures based on security and medical sources.