Russia's unconventional attacks against NATO "look like war" and allies must set new red lines that will trigger a retaliation if crossed, a former foreign minister has warned.

NATO Deputy Assistant Secretary General James Appathurai has issued a warning about Russia’s increasing hybrid warfare tactics amid fears of an escalation in its war with Ukraine.

General Mark Rutte says the military alliance will step up patrols in the Baltic Sea area as Finnish investigators work to establish whether a ship linked to Russia sabotaged undersea cables there this week.

NATO said on Friday it would boost its presence in the Baltic Sea after the suspected sabotage this week of an undersea power cable and four internet lines, while alliance member Estonia launched a naval operation to guard a parallel electricity link.

NATO will strengthen its presence in the Baltic Sea following the outage of the Estlink 2 submarine power cable, Secretary General Mark Rutte said on Friday after speaking to Finnish President Alexander Stubb.