US energy giant Chevron has signed another oil exploration deal in Iraq's autonomous Kurdistan region, it said on Monday, one of several contracts between Kurds and foreign energy firms that have enraged Baghdad.

The contract to explore the Qara Dagh field, in the south of the three-province region, is Chevron's third with Kurdish officials, who have signed a swathe of contracts with international oil companies to boost exploration and production of energy.

Iraq's central government, however, has slammed the deals as illegal on the grounds that they were not approved by the federal oil ministry, and last year barred Chevron from working in non-Kurdish parts of the country.

"Chevron will acquire an interest in and operatorship of the Qara Dagh block production sharing contract from the Kurdistan regional government," the company said in a statement issued from the Kurdish regional capital Arbil.

The block lies southeast of Arbil and is about 860 square kilometres (332 square miles) in total area, it said.

The American energy giant was awarded the exploration deal in January, its third in Iraqi Kurdistan after acquiring two others in July 2012.

The spat over oil contracts is one of a string between Baghdad and Arbil. Diplomats and analysts say the unresolved rows are among the biggest threats to Iraq's long-term stability.