The United States says it had a direct meeting with Iranian officials earlier this week over the alleged Iranian plot to kill the Saudi ambassador to the United States.

State Department spokeswoman Victoria Nuland told reporters in Washington the meeting was to make “absolutely clear” that the United States considers that type of behavior “unacceptable” and a violation of U.S. and international law.

She says 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 United States and Iran.

On Thursday, President Barack Obama warned Iranian officials they would face the “toughest sanctions” possible for what he described as their complicity in the alleged plot to kill Saudi envoy Adel al-Jubeir.

Mr. Obama called the alleged plot part of a pattern of “dangerous and reckless behavior.” He said the United States would not take any options off the table in dealing with Iran.

The United States has not had diplomatic relations with Iran since 1980.

Iran has denied the allegations, with one Iranian official calling the scenario “absurd.”

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

The United States announced this week it had charged Manssor Arbabsiar, a naturalized U.S. citizen, and Gholam Shakuri, a member of an elite Iranian military unit, with conspiring to carry out a bomb attack on the Saudi envoy.

Officials arrested Arbabsiar at New York's John F. Kennedy International Airport on September 29, but Shakuri is still at large.