Iraqi Prime Minister Nuri al-Maliki said on Wednesday the Kurdish-controlled city of Arbil was becoming an operations base for the Islamic State militant group that seized swathes of northern and western Iraq last month.

Maliki is under pressure as Sunni militants, led by the al Qaeda offshoot Islamic State, hold large parts of the north and west of the country and have threatened to march on the capital.

"We will never be silent about Arbil becoming a base for the operations of the Islamic State and Baathists and Al Qaeda and the terrorists," Maliki said in his weekly televised address.

Maliki's relationship with Kurdish President Massoud Barzani has deteriorated amid the sectarian insurgency that has threatened to split the country.

Barzani last week asked the parliament of the autonomous Kurdish region to plan a referendum on Kurdish independence, signalling his impatience with Baghdad.

Maliki, meanwhile, has accused the Kurds of exploiting the crisis to push for statehood.

Many Sunnis who fled the mostly Sunni northern city of Mosul during the militants' offensive have ended up in Arbil.

"These are politicians in the Sunni community and they have been deprived of participating in the political process," one senior Kurdish official said, speaking on condition of anonymity this week.-Reuters