Damage to a telecommunications cable between Sweden and Estonia earlier in October was caused by "external force", the Swedish government said Monday.
"It has been confirmed that the cable has been damaged through external force or tampering," the government said in a statement.
On October 17, the Swedish government said it had received information that a telecommunications cable linking the two countries had been damaged, without being able to identify the cause.
The cable is believed to have been damaged at the same time as a gas pipeline connecting Estonia and Finland, which authorities also believe to have been caused by "external" activity.
Last week, NATO said it was ramping up patrols in the Baltic Sea, including additional surveillance and reconnaissance flights, in response to the damage to the underwater infrastructure.
Ten northern European countries, including Sweden, Finland and Estonia, agreed this month to strengthen the surveillance of essential infrastructure following the shutdown of the Balticconnector gas pipeline in Finland.
"There is a spaghetti of cables, pipelines and infrastructure on the seabed that is absolutely fundamental for data traffic... and everything that is controlled digitally," Swedish Prime Minister Ulf Kristersson said on October 13, adding that "the vulnerabilities are much, much bigger nowadays".
On Friday, Finnish police said a Chinese ship was the focus of their investigation into suspected sabotage of the Balticconnector pipeline.
Last year, underwater explosions resulted in the rupture of three pipelines in the Baltic Sea responsible for the transportation of natural gas from Russia to Western Europe.