Russia on Friday accused Slovakia of breach of contract for handing over Soviet-era MiG-29 fighter planes to Ukraine.
Under a treaty signed in 1997, the central European country could not transfer the jets to another state without Russia's consent, the Federal Service for Military-Technical Cooperation in Moscow said.
Russian authorities cited an "unfriendly act" and a violation of Bratislava's international obligations as per the contract published on the Russian Foreign Ministry's website.
Amid opposition criticism of the jet transfer, the Slovakian leadership had not yet reacted publicly to Russia's charges, which the country's embassy in Bratislava also voiced earlier.
Slovakia passed four of the aircraft to Ukraine on Thursday, with nine more to follow "in the course of the next few weeks," the Defence Ministry in Bratislava told dpa. Three of the total of 13 aircraft are not operational and are to be used for spare parts.
Most of the jets were supplied by the Soviet Union to Czechoslovakia in the late 1980s. Following the break-up of the country, the Czech Republic and Slovakia divided up the aircraft, with the latter receiving more aircraft from Russia in the 1990s.
The Kremlin recently downplayed the value of the aircraft being supplied by Slovakia and Poland, saying that Ukraine was receiving redundant technology.
