• AP says White House rejects report on Saudi plan to act in Iraq if U.S. leaves
• Source says Saudi king "read riot act" to Vice President Dick Cheney about Iraq
• Saudi Arabia would support Sunnis in Iraq if the U.S. pulls out, the source says
• King Abdullah also is said to oppose talks between the U.S. and Iran

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WASHINGTON (CNN) -- Saudi Arabia's King Abdullah has warned Vice President Dick Cheney that Saudi Arabia would back the Sunnis if the United States pulls out of Iraq, according to a senior American official.

The official said the king "read the riot act" to the vice president when the two met last month in the Saudi capital, Riyadh.

The New York Times first reported the conversation Wednesday, saying Saudi support would include financial backing for minority Sunnis in the event of a civil war between them and Iraq's Shiite majority.

Violence between the two sects has exploded in waves of revenge killings since February's bombing of a revered Shiite mosque in Samarra, north of Baghdad.

The White House dismissed the report.