Iran's Supreme Leader Ayatollah Ali Khamenei says U.S. claims that Tehran supported an alleged assassination plot against a Saudi envoy are absurd.

The supreme leader accused the U.S. of making “unfounded” accusations against “a few Iranians in America” as part of an effort to isolate Iran.

He made the comments during a speech Saturday in a western province . The speech was carried on state television.

On Tuesday, the U.S. Justice Department announced it had broken up an alleged Iranian plot to assassinate Saudi Ambassador to the U.S. Adel al-Jubeir. Officials said the U.S. had filed charges against two Iranians for involvement in the plot. Officials said one suspect was part of Iran's elite Quds Force.

Saturday's comments from the supreme leader marked his first direct reaction to the claims, although lower-ranking Iranian officials had denied the charges earlier in the week.

On Friday, U.S. State Department spokeswoman Victoria Nuland said Washington had a direct meeting with Iranian officials this week over the alleged plot.

She told reporters the meeting was to make it “absolutely clear” that the U.S. considers that type of behavior “unacceptable” and a violation of U.S. and international law.

She said any effort by Iran to deny the meeting “speaks again” to how truthful Tehran is about such matters.

Iran's Mehr news agency on Friday quoted an official at Iran's U.N. mission as saying there has been no direct contact between the U.S. and Iran.

Also Friday, some U.S. lawmakers urged the government to step up the pressure on Iran. Several members of Congress said that sanctions against Tehran do not appear to be working and said stronger action is required.

Both Washington and Tehran have sent letters to the United Nations about the plot. The U.S. note said the alleged conspiracy was “conceived, sponsored and directed” by elements of the Iranian government. The Iranian letter expressed Tehran's “outrage” and strongly rejects what it calls “fabricated and baseless allegations.”