Crew on board an oil tanker accused of sabotaging undersea power and communications cables in the Baltic Sea were poised to cut other cables and pipelines when Finnish authorities boarded the vessel last month,

Estonian naval ships are taking part in stepped-up patrols in the Baltic Sea by NATO countries after undersea power and communications cables have been damaged in recent months.

"Had it continued for another 12 minutes, the carnage would have been much worse than the four basic cables that were there," Finnish President Alexander Stubb said.

Finnish police said on Tuesday they had recovered a lost anchor from the seabed as part of an investigation of suspected sabotage against power and internet cables in the Baltic Sea.