The Russian aircraft was flying from mainland Russia to the Kaliningrad enclave over international waters off Estonia's Baltic Sea coast, NATO explained in a statement posted on its website.

“Since there was no flight plan, neither was the plane in contact with air traffic control nor was it using its transponder, NATO's Northern Combined Air Operations Center in Uedem, Germany, ordered the F-16s to be launched and confirmed the details of the unknown aircraft”, detailed the Atlantic Alliance.

The Portuguese fighters, which had the first alert output on their second day of the mission, were launched from Šiauliai, in Lithuania.

“After identifying and escorting the Russian plane, the Portuguese fighters safely returned to Šiauliai. This was a routine event,” he added.

For the commander of the Portuguese detachment, Lieutenant Colonel José Dias, quoted in the statement, the operation was a demonstration of "the excellent commitment, dedication and professionalism of all the elements that make up the detachment".

Portugal leads the 62nd rotation of NATO's Baltic Air Policing mission. Four F-16s arrived early last week and assumed responsibility for protecting NATO's regional airspace alongside the F-16s of the Romanian Air Force on March 30, the Atlantic Alliance added.

Since the accession of Estonia, Latvia and Lithuania in 2004, NATO allies have taken turns deploying an air policing capability to Šiauliai to protect the territorial integrity of the three Baltic allies in a strong demonstration of Alliance cohesion and solidarity added the organisation.