The diplomat, whose name is said to be Abolfazl Eslami, is reportedly the former counselor of Iran's embassy in Tokyo.
Iranian opposition websites have reported that Eslami has said in a letter that “he’s disgusted by the violence against the people” and is thus resigning.
Eslami has reportedly called on other Iranian diplomats to join him in light of state repression in Iran.
RFE/RL has not been able to confirm the report.
Earlier this month, Mohammad Reza Heydari, former Iranian consul in Oslo, resigned from his post to protest Tehran's crackdown on pro-reform demonstrators and to show his solidarity with the goals of the opposition Green Movement.
Heydari, who is seeking political asylum in Norway, told RFE/RL's Radio Farda that he is planning to launch a campaign, “Green embassies,” to call on Iranian diplomats to join the Green Movement. Heydari said he’s already contacted a number of diplomats inside and outside Iran to convince them to join the movement.
On January 18, Iranian Foreign Minister Manuchehr Mottaki confirmed Heydari had resigned but said that Tehran did not accept his resignation.
Iranian opposition blogs have claimed that several Iranian diplomats have resigned in recent weeks without providing any names.
"The Times" of London quoted on January 16 a report by the Arabic television channel Al-Arabiya that said 27 Iranian diplomats had resigned in protest at the crackdown on the opposition, including one in Britain and two each in France and Germany.
The report has not been confirmed.
-- Golnaz Esfandiari