TEHRAN: Iran has complained to the United Nations about a U.S. accusation it tried to assassinate a Saudi diplomat, saying one of the alleged plotters Washington calls an Iranian military official is really a member of an anti-Tehran rebel group.

Foreign Minister Ali Akbar Salehi said on Saturday the plot was part of a multi-pronged U.S. strategy to smear Tehran, a process he said would continue next week when the U.N. nuclear agency publishes a report western diplomats say will contain new evidence about Iran's nuclear programme.

The complaint to U.N. Secretary-General Ban Ki-moon turned the U.S. accusation that Tehran supports terrorism back onto Washington, Salehi said.

"This letter contains our complaint about the plots of the United States, reliable information that we have of the U.S. involvement in those plots," he said in a news conference broadcast live on the English language channel Press TV.

On its website, Press TV reported the letter said a suspect who U.S. prosecutors have identified as an Iranian military official is actually a member of the exiled Iranian rebel group Mujahideen Khalq Organisation (MKO).

One of two men charged with plotting to kill the Saudi ambassador to Washington, 56-year-old Iranian-American Manssor Arbabsiar, pleaded not guilty at a court hearing in New York last month.

The second, Gholam Shakuri, is still at large and U.S. officials say he is a member of the Quds Force, an arm of Iran's Revolutionary Guards, who approved the plan to hire Mexican gangsters to murder Saudi Ambassador Adel al-Jubeir.

The semi-official Mehr news agency reported on Oct. 17 that Shakuri was a member of the MKO, also known as the People's Mujahideen Organisation of Iran (PMOI), based in Iraq and listed as a terrorist group by the United States.

Citing "informed sources", Mehr said Shakuri had travelled to Washington and to the MKO base at Camp Ashraf in Iraq.

Iranian officials did not initially comment on the report which said Interpol had discovered Shakuri's true identity, but Press TV reported on Saturday it was now in the letter delivered to Ban.

Washington is using what it says was a foiled plot to help bolster international support to tighten sanctions on Iran which it accuses of developing nuclear weapons and sponsoring terrorism, charges denied by Tehran.

Israeli and western media have increased speculation in recent days that Israel might launch a strike on Iran's nuclear sites. Some analysts say that, rather than any firm evidence military action is imminent, the chatter reflects efforts to increase diplomatic pressure on Tehran.

Salehi said Iran did not fear possible revelations in a report to be issued by the International Atomic Energy Agency (IAEA) on Wednesday that western diplomats say will make a "compelling case" the Iranian nuclear programme is not entirely peaceful.

"They are claiming that they are going to publish new documents. We know what the truth is -- let them publish them and we'll see what happens. Will they not be called into question as an agency that is under pressure by foreign powers?" Salehi said.

The IAEA report, the assassination plot and accusations about human rights abuses were a "three-pronged attack from

the West against Iran ... just an assault to pressure Iran into subjugation," he said.

Salehi repeated the stance of Supreme Leader Ayatollah Ali Khamenei who has said Iran has 100 "undeniable documents" proving U.S. involvement in terrorism. (Additional reporting by Mitra Amiri; Editing by Sophie Hares)