Iran summoned the French ambassador on Tuesday to protest about a meeting held in Paris by Iranians in exile who seek the overthrow of the Islamic Republic.
The rally was held on Saturday by the National Council of Resistance of Iran, the political wing of the Mujahideen-e-Khalq Organisation (MKO), a group that waged armed struggle against the Iranian government after the 1979 revolution and assassinated dozens of its top officials.
The MKO sided with Saddam Hussein during Iraq's war with Iran in the 1980s but fell out of favour with Baghdad after he was toppled by the U.S.-led invasion in 2003.
"The gathering held by those whose hands are stained by the blood of the Iranian people ... is unacceptable," Abolghassem Delfi, director of the West Europe department at Iran's Foreign Ministry, was quoted as saying by state news agency IRNA.
The Paris rally was addressed by Prince Turki al-Faisal, former chief of Saudi Arabia's intelligence services, who openly supported MKO's struggle against the Iranian government.
Shia Muslim power Iran and Saudi Arabia, bastion of Sunni Islam, are longstanding religious and political rivals.