NATO countries on the Baltic Sea met in Helsinki on Tuesday, looking to boost security following the suspected sabotage of undersea cables, widely blamed on Russia.

They are expected to announce a NATO patrol mission monitoring activity "below, above, and on the sea surface", researcher Iro Sarkka of the Finnish Institute of International Affairs told AFP.

Several undersea telecom and power cables have been severed in the Baltic Sea in recent months, with experts and politicians accusing Russia of orchestrating a hybrid war.

The sabotage has been blamed on a "shadow fleet" of vessels -- often ageing and operating under opaque ownership -- that carry Russian crude oil and petroleum products, embargoed since the invasion of Ukraine.

Addressing the European Parliament, NATO Secretary General Mark Rutte stressed on Monday the need to make clear that "such hostile actions" and such efforts "will not go unanswered".

"We will also strengthen NATO's military presence in the region, and of course, we will discuss the shadow fleet and what to do about it. So we are responding........

© International Business Times