Iraq on Sunday urged foreign countries to stop importing crude directly from its autonomous Kurdistan region and to restrict oil trading to the central government.
The call, published in statement from Prime Minister Haider al-Abadi's office, came in retaliation for the Kurdistan Regional Government's plan to hold a referendum on independence on Monday.
The central government's statement seems to be directed primarily at Turkey, the transit country for all the crude produced in Kurdistan. The crude is taken by pipeline to the Turkish Mediterranean coast for export.
Baghdad "asks the neighboring countries and the countries of the world to deal exclusively with the federal government of Iraq in regards to entry posts and oil," the statement said.
The Iraqi government has always opposed independent sales of crude by the KRG, and tried on many occasions to block Kurdish oil shipments.
Long-standing disputes over land and oil resources are among the main reasons cited by the KRG to ask for independence.
Iraqi Kurdistan produces around 650,000 barrels per day of crude from its fields, including around 150,000 from the disputed areas of Kirkuk.
The region's production volumes represent 15 percent of total Iraqi output and around 0.7 percent of global oil production. The KRG aspires to raise production to over 1 million barrels per day by the end of this decade.
Kurdish oil production has been dominated by mid-sized oil companies such as Genel, DNO, Gulf Keystone and Dana Gas. Major oil companies such as Chevron, Exxon Mobil and Rosneft also have projects in Kurdistan but they are mostly at an exploration stage.
However, Rosneft, Russia's state oil major, has lent over $1 billion to the KRG guaranteed by oil sales and committed a total of $4 billion to various projects in Kurdistan.