"There is a transit in our waters of ships from the Russian Federation, an increasingly intense transit, from North to South and from South to North", Admiral Henrique Gouveia e Melo told journalists, in statements broadcast on the channel CNN television.

According to the admiral, during a very short period of time three warships (two frigates and a corvette), two refuelling ships, three scientific research ships and even "a ship that carries out espionage, normally electronic espionage" passed through Portuguese waters.

Gouveia e Melo explained that the Navy monitors this flow of Russian ships with strict surveillance.

"Our response to this is to follow them, control them, keep them under constant pressure with our constant presence," he told reporters.