Iraq has accused Kurdish forces of seizing two northern oil fields near the disputed city of Kirkuk.

The accusations come as relations between Baghdad and the autonomous Kurdistan region worsen.

The Kurdish regional administration rejected the charge, which marks an escalation of tensions that have cast a shadow over efforts to form a national unity government to counter Islamic State insurgents.

"The oil ministry strongly condemns the seizure and control of crude oil (wells) in the Kirkuk and Bey Hassan oil fields this morning by groups of Kurdish peshmerga forces," Iraq's oil ministry said in a statement.

"The oil ministry strongly warns the Kurdistan region of the danger of this irresponsible behaviour which violates the constitution and the national wealth, and disregards the federal authorities and threatens national unity."

The two oil fields are said to have a combined daily output capacity of some 400,000 barrels per day, a ministry spokesman said.

Halkurd Mulla Ali, the spokesman for the ministry responsible for Kurdish peshmerga forces, told AFP that "peshmerga forces have not approached the oil fields in Kirkuk" province.

Yesterday the Kurds said Iraqi Prime Minister Nuri al-Maliki was "hysterical" and not fit to run the country, after he accused them of harbouring militants in territory they control.

Iraqi lawmakers are due to meet on Sunday for a parliamentary session meant to revive flagging efforts to form a new government.

The only other time parliament has met since April polls ended with MPs exchanging heckles and others walking out.

Kurdish troops moved into disputed areas vacated by federal forces that failed to stop a Sunni militant onslaught that began on 9 June.

The Kurds have since said those swathes of land were theirs to keep, and announced plans to hold a referendum on independence.