Several senior Russian missile specialists have visited Iran over the past year as the Islamic Republic deepened its defense cooperation with Moscow, a review of travel records and employment data indicates.

The seven weapons experts were booked to travel from Moscow to Tehran aboard two flights on April 24 and Sept. 17 last year, according to documents detailing the two group bookings as well as the passenger manifest for the second flight.

The booking records include the men's passport numbers, with six of the seven having the prefix "20." That denotes a passport used for official state business, issued to government officials on foreign work trips and military personnel stationed abroad, according to an edict published by the Russian government and a document on the Russian foreign ministry's website.