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.

Iraqi Kurds are expected to vote for independence in a referendum on Monday that neighboring countries and Western powers fear could break up the country and stir broader regional ethnic and sectarian conflict.

Iran halted flights to and from Kurdish regions in northern Iraq on Sunday in retaliation to a plan by the autonomous Kurdistan Regional Government (KRG) to hold a referendum on independence. It also started wargames at the Kurdish border.

The United States “strongly opposes” the planned independence referendum by Iraqi Kurds and urges Iraqi Kurdish leaders to engage in negotiations with the Baghdad government instead, the U.S. State Department said on Wednesday.

Saudi Arabia on Wednesday urged Iraqi Kurdish leader Massud Barzani to call off a planned referendum on independence for his autonomous region to avoid further "crises" in Iraq and the region.

Iraqi Prime Minister Haider Al-Abadi described the Kurdistan region’s planned referendum on independence as “unconstitutional” on Tuesday, hours after parliament voted against the regional plebiscite.