Russia, the only major power that has not called on Iraq's Kurds to cancel a referendum on independence next week, has swiftly become the top funder of Kurdish oil and gas deals, with as much as $4 billion pledged in less than a year, industry sources say.

Washington, European countries, Turkey and Iran have all lined up to oppose a move by Iraq's Kurds to hold a Sept. 25 independence referendum, which the Kurds consider the culmination of decades of struggle for a state of their own, but Iraq calls a violation of its constitution.

This week, the White House issued a statement calling the planned vote "provocative and destabilizing," noting that it will take place not only within the autonomous Kurdish region itself but on territory that is disputed.