Several senior Russian missile specialists have visited Iran over the past year as the Islamic Republic has deepened its defence cooperation with Moscow, a Reuters 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 September 17 last year, according to documents detailing the two group bookings as well as the passenger manifest for the second flight.

A senior Iranian defence ministry official said Russian missile experts had made multiple visits to Iranian missile production sites last year, including two underground facilities, with some of the visits taking place in September. The official, who requested anonymity to discuss security matters, didn’t identify the sites.

A Western defence official, who monitors Iran’s defence cooperation with Russia and also requested anonymity, said an unspecified number of Russian missile experts visited an Iranian missile base, about 15 km (9 miles) west of the port of Amirabad on Iran’s Caspian Sea coast, in September.