Jens Stoltenberg made the statement in Brussels on Wednesday, a day after officials confirmed damage to the pipeline and an accompanying telecommunications cable, news outlets reported.
Finnish authorities investigating the disruption have said it was probably caused by "outside activity."
Investigators have found "external marks" on the seabed beside the damaged pipeline, according to news outlets.
The damage was probably caused “by mechanical force, not an explosion,” Finnish officials said.
The leak is expected to take at least five months to fix and LNG supplies could be resumed in April, towards the end of the heating season, Poland’s biznesalert.pl website reported.
NATO’s Stoltenberg told reporters: "The important thing now is to establish what happened and how this could happen.”
He declared: "If it is proven to be a deliberate attack on NATO critical infrastructure, then this will be, of course, serious, but it will also be met by a united and determined response from NATO."
Meanwhile, Kremlin spokesman Dmitry Peskov described the incident as “disturbing,” adding that the attack on the Russia-to-Germany Nord Stream gas pipelines in September 2022 “set a dangerous precedent,” the Reuters news agency reported.
Since then, there has been a series of further incidents involving Europe’s energy, telecommunications and railway infrastructure, prompting the European Union and NATO to strengthen cooperation in “protecting critical infrastructure,” biznesalert.pl reported.
Under the EU’s Critical Entities Resilience (CER) directive, operators of such facilities are required to “take appropriate measures to ensure their resilience.”
The disruption to the Balticconnector pipeline occurred a few months after Finland joined the NATO alliance, biznesalert.pl noted.
Russia invaded Ukraine on February 24, 2022, launching the largest military campaign in Europe since World War II.
Thursday is day 596 of Russia’s war on Ukraine.
(pm/gs)
Source: biznesalert.pl, Reuters, CER Directive