HELSINKI (AP) — Finnish President Sauli Niinistö says damage to an undersea gas pipeline and telecommunications cable connecting Finland and Estonia appears to have been caused by “external activity.”

Finnish and Estonian gas system operators on Sunday said they noted an unusual drop in pressure in the Balticconnector pipeline after which they shut down the gas flow.

The Finnish government on Tuesday said there was damage both to the gas pipeline and to a telecommunications cable between the two NATO countries.

“The damage to the underwater infrastructure has been taken seriously and the causes have been under investigation since Sunday,” Niinistö said. “The state authorities have been kept closely informed of the situation.”

“It is likely that the damage to both the gas pipeline and the telecommunications cable is the result of external activity,” he said. “The cause of the damage is not yet clear and the investigation is continuing in cooperation between Finland and Estonia.”

Niinistö said he was in contact with allies and partners, including NATO Secretary-General Jens Stoltenberg.

Stoltenberg wrote on X, formerly known as Twitter, that he had spoken with Niinistö ”on damage to undersea infrastructure.” He said NATO is sharing information and “stands ready to support Allies concerned.”

The pipeline incident was likely to be put on the agenda for a NATO defense ministers meeting in Brussels on Wednesday and Thursday.

Finnish Prime Minister Petteri Orpo was to hold a news conference about the situation later Tuesday.

Estonia’s Navy told The Associated Press that they were conducting an investigation on the pipeline together with the Finnish military in the Gulf of Finland. They wouldn’t comment further, saying the operation was led by the Finns.

The 77-kilometer-long (48-mile-long) Balticconnector pipeline runs across the Gulf of Finland from the Finnish city of Inkoo to the Estonian port of Paldiski. It is bi-directional, transferring natural gas between Finland and Estonia depending on demand and supply. Most of the gas that was flowing in the pipeline early Sunday before closure was going from Finland to Estonia, from where it was forwarded to Latvia, Estonia’s gas system operator Elering said.

The pipeline started commercial operations at the beginning of 2020.

Gasgrid Finland said the Finnish gas system is stable and the supply of gas has been secured through the offshore support vessel Exemplar — a floating liquefied natural gas terminal at the southern Finnish port of Inkoo.

Elering said Estonian consumers were receiving gas from Latvia after the shutdown of the pipeline.

In September 2022, the Nord Stream gas pipelines running between Germany and Russia in the Baltic Sea were hit by explosions in an incident deemed to be a sabotage. A total of four gas leaks were discovered on the Nord Stream 1 and Nord Stream 2 pipelines. The case remains unsolved.

___ Associated Press writer Jan M. Olsen in Copenhagen, Denmark, and Lorne Cook in Brussels contributed to this report