Sweden on Saturday accused Russia of violating its airspace and warned Moscow to respect Swedish sovereignty, weeks before the Nordic country is expected to make an official bid to join NATO, a move Russia strongly opposes.

The incident involving the Russian aircraft took place on Friday evening, when a Russian Antonov An-30 reconnaissance plan was detected east of the Danish island of Bornholm. The plane subsequently went on to briefly violate Swedish airspace before it was escorted out by the Swedish air force.

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“A Russian AN-30 propeller plane violated Swedish airspace on Friday evening. Swedish fighter jets followed the incident and photographed the plane,” Sweden’s defence ministry said in a statement.

With Sweden’s official bid to join NATO looming in the distance, Swedish Defence Minister Peter Hultqvist strongly condemned the incident and promised to take diplomatic action against Russia.

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“We will, of course, act diplomatically against this,” Hultqvist told Swedish newspaper Aftonbladet, adding, “This action is unprofessional and given the overall security situation, extremely inappropriate. Swedish sovereignty must always be respected.”

Indeed, the “overall security situation” in Europe following Russia’s invasion of Ukraine has deteriorated to a point where Sweden and Finland are on the verge of applying for a NATO membership, a move that was once unthinkable.

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In response, Russia has threatened to deploy nuclear weapons in the Baltic as it looks to take a stand against NATO’s expansion in Europe, which, incidentally, was cited by Russian President Vladimir Putin as one of the reasons behind the troop build-up around Ukraine prior to the beginning of the Russian invasion on February 24.