The two sides have clashed over how oil revenues should be distributed and Kurdish authorities have said they will not resume crude exports until Baghdad pays the foreign energy companies which are pumping the oil.

"Oil exports from Kurdistan's fields have been stopped until an agreement is reached with the Iraqi oil ministry for mechanisms to pay the dues of the oil companies working in the region," Ashti al-Hawrami told AFP.

Hawrami said in a letter posted on the regional government's website that Norway's DNO and Turkey's Genel Enerji had not been paid for their exports because the oil sale revenues went directly to Baghdad.

The oil ministry in Baghdad, however, said that as it had not approved the contracts with the firms operating in Kurdistan, it would only give the Kurdish region its allotted share of central government revenues.

"The Iraqi government and the ministry did not sign any contracts with these companies and have not seen the details of the contracts agreed by the region," said a senior ministry source, speaking on condition of anonymity.

"The agreement with the region is for the proceeds of oil exported from Kurdistan to be deposited in the central government budget, and the region gets its share of the central budget."

Around 17 percent of federal spending is allotted to the Kurdish region in northern Iraq.

Ministry spokesman Assem Jihad said the ministry's responsibility was to "export Iraqi oil ... and then deposit the revenues with the central government."

The oil ministry and Iraqi Kurdistan are at loggerheads over how international companies involved in the tapping of the nation's vast energy reserves should be paid.

Baghdad has repeatedly said it is opposed to the Kurds signing their own contracts, a position which Kurdish officials have largely disregarded by signing dozens of agreements with foreign firms.

However, the central government in May gave its approval for Iraqi Kurdistan to begin exporting oil extracted by the companies which had signed deals with Arbil, the region's capital.

Iraq has the world's third largest proven reserves of oil, with more than 115 billion barrels, behind only Saudi Arabia and Iran.