The Swedish Armed Forces reported four Russian fighter planes briefly crossed Swedish territory over the Baltic Sea on Wednesday, prompting a strong criticism from Sweden’s defense minister.

Two Russian SU27 and two SU24 fighter planes temporarily invaded Swedish airspace east of the Swedish island of Gotland in the Baltic Sea, according to Sweden’s Armed Forces, who added that Swedish JAS 39 Gripen fighters were dispatched to document the breach.

“Of course, the Russian breach of Swedish airspace is extremely unacceptable,” Defense Minister Peter Hultqvist told TT. “Sweden will respond with a strong diplomatic response. Swedish sovereignty and territory must be respected at all times.”

Sweden’s Armed Forces said the situation was under control and that the incident showed preparedness was good.

“In the light of the current situation we view this event very seriously,” it said on its website,

Sweden on Sunday said it would send military aid, including 5,000 anti-tank weapons to Ukraine, the first time since 1939 that Sweden has sent weapons to a country at war.