WASHINGTON: Saudi Arabia's former ambassador to the U.S. said Tuesday there was "ample and heinous" evidence that Iran was behind an alleged plot to kill the current Saudi envoy to Washington.

Prince Turki al-Faisal, who also once served as Saudi Arabia's intelligence chief, told reporters that if Tehran failed to prosecute Iranians linked to the plot, Riyadh may take the case to the United Nations.

"We have seen ample and heinous evidence in the uncovering of an assassination plot against the Saudi ambassador to the United States," he said, adding the evidence "indicates the depths of depravity and unreason to which the Ahmadinejad regime has sunk. Fortunately, this plot was foiled."

Turki also said it was "inevitable" that Syria's president will step down in the face of growing popular opposition.

The Saudi prince is no longer a government official and said he was speaking as a private citizen. But he is an influential member of the royal family and serves as chairman of the King Faisal Center for Research and Islamic Studies.

The U.S. charged in October that agents linked to Iran's Quds Force - an elite wing of the powerful Revolutionary Guard - were involved in a plot to kill Saudi Ambassador to the U.S. Adel al-Jubeir. Iran has called the accusation "baseless."

Turki called the plot "the tip of the iceberg," saying Iran was "meddling" in the affairs of many other countries, including Lebanon, Turkey, Pakistan and especially Iraq. The Saudi government has also accused a terror cell linked to Iran of plotting to blow up its embassy in Bahrain, as well as the causeway linking the island kingdom to Saudi Arabia.

The U.S. and other nations suspect that Iran is using its civilian nuclear work as a cover for a weapons program, but Iran insists that its nuclear ambitions are strictly peaceful. The U.S. has used sanctions and diplomacy to pressure Iran on the issue but has long refused to rule out military action saying that all options are on the table.

In a secret diplomatic cable made public by WikiLeaks, Saudi King Abdullah urged Washington to strike at Iran and "cut off the head of the snake." But Turki dismissed the document, telling reporters that Saudi Arabia supports sanctions and diplomatic pressure against Iran but not a military strike.

Turki said military action would only stiffen Iran's resolve, rally support for the regime and at best delay, but not halt, the nuclear program. "Such an act I think would be foolish, and to undertake it I think would be tragic," he said.