"The Islamic Republic of Iran strongly condemns the US government’s illegal measures against the Iranian people, including its support for and financing of Monafeqin (MKO) as a terrorist group," the letter said, as quoted by Tasnim News Agency.
According to the media outlet, the letter also expressed indignation over the fact that senior US figures such as President Donald Trump's lawyer Rudy Giuliani and former Speaker of the House of Representatives Newt Gingrich attended a PMOI gathering on June 30.
The ambassador also denounced the US decision to remove PMOI from the list of terrorist organizations in 2012 as a double standard with regard to the war on terrorism.
READ MORE: Tehran Lodges Protest With France, Germany Over Detention of Iranian Diplomat
The Iranian authorities have accused the group of multiple terrorist attacks and linked it with the recent story around the detained diplomat from the Iranian Embassy in Vienna. The diplomat was detained on suspicion of complicity in plotting a foiled bomb attack on a rally of an exiled Iranian opposition organization, the National Council of Resistance of Iran (NCRI), affiliated with PMOI. The meeting took place in the outskirts of Paris on June 30.