"Fifteen armed men travelling in two vehicles entered our area in the centre of the city at around 1:00 pm (1000 GMT)," said Jafaar Khayat, spokesman for the Goran (Change) party.

"They removed took all the posters of our candidates and replaced them with posters of President Talabani and Kosrat Rasul," who is a senior official in Talabani's Patriotic Union of Kurdistan (PUK).

Khayat added that one of the party's guards was beaten with the butt of a rifle, and said that the people behind the attack left before police arrived at the scene.

Arbil police chief General Abdul Khaleq Talaat confirmed the incident and said: "We were able to identify the people behind the attack and have issued warrants for their arrest."

The Goran bloc, which is primarily composed of ex-PUK members, emerged as the region's first credible opposition in regional elections last July, after nearly two decades of dominance by the PUK and the Kurdistan Democratic Party (KDP) of regional president Massud Barzani.

Several incidents have thus far marred campaigning in Iraqi Kurdistan, and Iraq's election commission has imposed a 9:00 pm curfew on campaigning in Sulaimaniyah province, which borders Arbil, after a number of violent incidents were reported.