A man holds a Kurdish flag with a picture of Iraqi Kurdish leader Masoud Barzani during a gathering to support next week's referendum in Iraq, at Martyrs Square in Downtown Beirut, Lebanon, Sunday, Sept. 17, 2017. Iraq's Kurdish region plans to hold the referendum on Sept. 25 to gauge support for independence from Iraq for the autonomous region. (AP Photo/Hassan Ammar)

Kirkuk - Four Iraqi Kurdish soldiers were killed in an explosion in the province of Kirkuk, an area where a contentious independence referendum is set to be held on Monday, Iraqi police said.

Seven other Kurdish Peshmerga troops were injured in the blast that hit their patrol car late on Saturday in Kirkuk, 250 kilometres north of the capital Baghdad, police added.

So far, there has been no claim of responsibility.

Kirkuk, an oil-rich region, is one of several disputed areas between Iraq's autonomous region of Kurdistan and Baghdad.

In 2014, Kurdish forces seized Kirkuk after Iraqi troops withdrew from the region in the face of a blitz by the Islamic State extremist militia. 

The Kurdistan government has said that Monday's referendum will cover the territory as well as other Kurd-controlled areas in northern Iraq including ethnically mixed Kirkuk.

Baghdad has condemned the vote as unconstitutional.

The referendum has also raised alarm of Iraq's neighbours - Turkey, Iran and Syria - over concerns it could encourage their own Kurdish minorities to break away. Turkey has warned it may impose sanctions on Kurdistan over the plebiscite.

The UN has warned of the vote's "potentially destabilizing effect," while the US has said it could fuel regional unrest and distract attention from ongoing campaigns to rout Islamic State in Iraq and Syria.