Russia accused Slovakia on Friday of breaching a contract over the delivery of Soviet-made MiG-29 fighter jets to Ukraine.

The Federal Service for Military-Technical Cooperation of the Russian Federation (FSVTS), which is responsible for the agreements on armament programs concluded by Moscow with the governments of other states, underlines that Slovakia was bound by a 1997 treaty not to deliver MiG-29s to another country without consent of the Kremlin.

Moscow called Slovakia’s hostile action a violation of its international obligations, which stem from the convention published on the Russian Foreign Ministry’s website.

Despite strong opposition criticism, the Slovak government has yet to react to Moscow’s accusations, which were also voiced by the Russian embassy in Bratislava.

Slovakia delivered four MiG-29 fighter jets to Ukraine on Thursday, with nine more to follow “in the coming weeks”, according to the defense ministry.

Three out of a total of 13 MiG-29s from Slovakia are not operationally ready and will be used for spare parts, the German News Agency (dpa) points out.

The majority of fighter aircraft of this type were delivered by the Soviet Union to Czechoslovakia in the late 1980s. After the breakup of the country, the Czech Republic and Slovakia divided the aircraft, with the latter acquiring more from Russia during the 1990s.