The shooters targeted the offices of the Kurdistan Democratic Party (KDP) in the town of Jalawla, 160 kilometres (100 miles) northeast of Baghdad, overnight.

The KDP is one of two main parties in the autonomous Iraqi region of Kurdistan, along with the Patriotic Union of Kurdistan and they have dominated its politics for decades.

Kurdish leaders have long demanded that their region, comprising three provinces, be expanded to include historically Kurdish-inhabited parts of Nineveh and Diyala provinces as well as all of Kirkuk.

Baghdad, however, says the Kurdish region's borders should not extend past Arbil, Sulaimaniyah and Dohuk provinces, in a dispute that observers warn could lead to wider conflict.

General Ray Odierno, the top US commander in Iraq, said on Monday that the United States was discussing arrangements that could see its troops work alongside Iraqi and Kurdish forces to promote confidence in disputed areas of northern Iraq, including Diyala.