Bulgaria’s State Agency for National Security has reportedly expelled two Russian diplomats for collecting information on the military’s procurement of F-16 Block 70 jets.

The officials, Sergei Nikolashin and Vadim Bykov, were also gathering data regarding Sofia’s plan to acquire combat drones, Bulgarian newspaper 24 Chasa reported.

The pair were given 72 hours to leave the European Union country, after Ivan Geshev, the Bulgarian public prosecutor, alleged they had been seeking out classified information on military modernization plans since 2016. The state secrets were collected with help from two Bulgarian nationals, to be passed on to Russian intelligence.

Bulgarian Air Force largely relies on MiG-29 jets but is expected to soon take delivery of eight U.S.-made F-16 jets bought last July.

Sofia’s relations with Moscow had soured even ahead of the recent spying spats after three Russian nationals were charged over the attempted poisoning in 2015 of a Bulgarian arms manufacturer, Emilian Gebrev, his son and another associate.