Abu Omar al-Baghdadi, who leads the group Islamic State in Iraq , said his Sunni fighters have been preparing for four years to wage a battle against Shiite-dominated Iran.

"We are giving the Persians, and especially the rulers of Iran, a two-month period to end all kinds of support for the Iraqi Shiite government and to stop direct and indirect intervention ... otherwise a severe war is waiting for you," he said in the 50-minute audiotape released Sunday. The tape, which could not be independently verified, was posted on a Web site commonly used by insurgent groups.

Iraq's Shiite-led government is backed by the U.S. but closely allied to Iran. The United States accuses Iran of arming and financing Shiite militias in Iraq — charges Tehran denies.

In the recording, al-Baghdadi also gave Sunnis and Arab countries doing business in Iran or with Iranians a two-month deadline to cease their ties.

"We advise and warn every Sunni businessman inside Iran or in Arab countries especially in the Gulf not to take partnership with any Shiite Iranian businessman — this is part of the two-month period," he said.