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.

Nations on the Baltic Sea, along with NATO, have stepped up security after a third incident of suspected sabotage to underwater infrastructure in a month.

Officials say the damage to Estlink 2, a power connection with the capacity to provide half of Estonia's winter electricity needs, did not disrupt service, although it did drive up energy prices in the country and the other Baltic nations.