Iran's Supreme Leader Ayatollah Ali Khamenei said on Saturday US accusations that two Iranians planned to assassinate the Saudi Arabian ambassador to Washington were "meaningless", state TV reported.
"A meaningless and nonsensical accusation has been raised against a few Iranians in America, which was made into an excuse to present the Islamic Republic as a supporter of terrorism," Khamenei told a crowd in the western province of Kermanshah.
"It didn't work, it won't work," he said.
Iran's English-language Press TV quoted Foreign Ministry spokesman Ramin Mehmanparast as saying the US allegations were "untrue and baseless".
"It is a comedy show fabricated by America," he said. The relationship between Iran and Saudi Arabia was based on "mutual respect" and could not be harmed by "fabricating such baseless claims".
US authorities say they broke up a plot to bomb the Israeli and Saudi Arabian embassies in Washington and assassinate the Saudi ambassador.
The alleged plotters were identified as Manssor Arbabsiar and Gholam Shakuri -- both originally from Iran -- in a criminal complaint unsealed in federal court in New York City.
The United States has said it held rare direct contacts with Iran over the allegations. An Iranian news agency quoted an Iranian official at the UN as denying that.
"I will again confirm that we did meet with the Iranians," State Department spokeswoman Victoria Nuland said on Friday.
"They know that very well, and any efforts on their part to deny it speaks again to how truthful they are about any of these sorts of matters."
Iran Saudi Tension
Political tension between Iran and Saudi Arabia has been increasing since Saudi forces intervened in March to help Bahrain's Sunni rulers crush pro-reform demonstrations backed by the Shi'ite majority.
Iran and the United State are at odds over Tehran's disputed nuclear programme, which Washington and its allies say is a cover to build bombs.
Tehran denies this, saying it needs nuclear technology to generate electricity to meet its booming domestic need. The United States and Israel, which Iran refuses to recognise, have not ruled out military action if diplomacy fails to resolve the row with Iran.