Saudi Arabia and the United States traded charges with Iran on Wednesday over an alleged plot to kill the Saudi ambassador to Washington, deepening divisions and sharpening a contest for power in the oil-rich Gulf.
The Saudis, long at odds with Tehran, said Iran would "pay the price" for an exotic plot described by U.S. officials to assassinate their ambassador. The United States threatened further sanctions on Iran, while Tehran called the accusation a fabrication designed to sow discord in the region.
In Washington, U.S. officials said it was "more than likely" that Iran's supreme leader, Ayatollah Ali Khamanei, and the head of its elite Quds force knew of the alleged plot. But the officials acknowledged that they had no hard evidence for the claim.
The American officials, speaking on condition of anonymity, also said it was possible that Iranian President Mahmoud Ahmadinejad did not know.
President Barack Obama spoke on Wednesday to Saudi King Abdullah about the alleged plot, the White House said.
Speaking in London, Saudi prince Turki al-Faisal, himself a former ambassador to Washington, said: "The burden of proof is overwhelming ... and clearly shows official Iranian responsibility for this. Somebody in Iran will have to pay the price."
Tehran said the allegations threaten stability in the Gulf -- where Saudi Arabia and Iran, the biggest regional powers, are fierce rivals and Washington has a huge military presence.
Ali Larijani, Iran's parliament speaker, said the "fabricated allegations" aimed to divert attention from revolts in the region and turn Muslim countries against each other.