Iraqi oil minister Jabar al-Luaibi said he had sought clarifications from Russia's biggest oil company Rosneft about contracts it signed with the semi-autonomous Kurdistan region.

Rosneft "assured that the contracts are preliminary and not ready for implementation," the minister told reporters in Baghdad, giving no further details.

Rosneft agreed on Thursday to take control of Iraqi Kurdistan's main oil pipeline, boosting its investment in the autonomous region to $3.5 billion.

The Iraqi government has warned companies against signing deals with the Kurdistan region and Baghdad's forces this week wrested control of the oil-rich Kirkuk from Kurdish forces.

Rosneft agreed on Thursday to take control of Iraqi Kurdistan's main oil pipeline, boosting its investment in the autonomous region to $3.5 billion.

Rosneft will be investing in expanding the pipeline hoping to boost its capacity by a third to 950,000 barrels per day. That is the equivalent of about 1 percent of global supply.

The pipeline usually carries 600,000 bpd but volumes dropped to just over 200,000 bpd this week after Iraqi forces took over the region of Kirkuk.

The pipeline carries crude from Kirkuk and other fields in northern Iraqi to the Turkish Mediterranean port of Ceyhan.