TEHRAN - Iran's Supreme Leader Ayatollah Ali Khamenei warned on Sunday that Tehran would respond robustly to any "inappropriate measure" by Western powers linked to an alleged Iranian plot to kill the Saudi ambassador to Washington, state television reported.

"Any inappropriate measure against Iran, whether political or security-related, will be strongly confronted by the Iranian nation," Khamenei said, in a clear reference to US allegations that two men with links to Iran's security forces had planned to assassinate the Saudi ambassador to the United States.

Iran says the allegation is without foundation and has been cynically engineered to further isolate Tehran -- whose disputed nuclear programme has triggered several rounds of international sanctions against it.