Foreign Minister Manouchehr Mottaki said Iran was "taking all the necessary steps" to solve the case of former Deputy Defense Minister Ali Reza Asgari, 63, who went missing after checking into an Istanbul hotel on February 7.
"A director-general from the (Foreign) Ministry has traveled to Turkey (to follow up the case). We have asked Turkey to investigate Asgari's case," IRNA quoted Mottaki as saying.
Iranian and Turkish officials were not immediately available for comment.
Turkey's Hurriyet daily reported Asgari was involved in nuclear work but did not give a source.
Iran is at odds with the West over its disputed nuclear program, which Tehran insists is only for generating electricity.
Six world powers are considering widening sanctions against Iran after it ignored a February 21 UN Security Council deadline to stop its uranium enrichment work, which the West believes Iran is using to make atomic bombs.