The North Atlantic Treaty Organization said Thursday it will increase patrols in the Baltic Sea after damage to underwater infrastructure between alliance members in the area.

"The increased measures include additional surveillance and reconnaissance flights, including with maritime patrol aircraft, NATO AWACS planes, and drones," the military alliance said in a statement.

"A fleet of four NATO minehunters is also being dispatched to the area," it added.

The move comes after a natural gas pipeline between Finland and Estonia and a telecommunications cable between Sweden and Estonia were damaged.

"We continue to monitor the situation closely, and we remain in close contact with our Allies Estonia and Finland, and our partner Sweden," NATO spokesperson Dylan White said.

"NATO will continue to adapt its maritime posture in the Baltic Sea and will take all necessary steps to keep allies safe."

Finland last week said a leak at the Balticconnector pipeline was caused by "external" activity, prompting fears of possible sabotage amid heightened tensions with Russia.

Finnish police said Thursday they had concluded dives to probe the leak, but they remain tight-lipped on the outcome of their investigation.

NATO chief Jens Stoltenberg said the military alliance would offer a "determined response" if it was shown the incident was a deliberate attack.