Germany says it suspects that damage to two undersea fibre-optic communication cables in the Baltic Sea was an act of sabotage.

Two cables, one between Finland and Germany, the other between Sweden and Lithuania, were severed on Sunday and Monday.

Though authorities initially declined to speculate, the incidents had raised suspicions of a malicious attack.

“No one believes that the cables were accidentally damaged. I also don’t want to believe that the ships’ anchors caused the damage by accident,” German defence minister, Boris Pistorius, said on Tuesday. “We have to assume, without certain information, that the damage is caused by sabotage.”

The Guardian reports: Sweden’s civil-defence minister, Carl-Oskar Bohlin, said a preliminary investigation into sabotage was under way. “There are ship movements that correspond to this crime on maritime surveillance, therefore a preliminary investigation into sabotage has been initiated,” he told TV4.

Sweden and Finland have announced they will launch a joint investigation.

The first of the suspected attacks was on a 135-mile (218km) internet link between Lithuania and the island of Gotland in Sweden at about 8am GMT on Sunday, the telecoms company Telia Lietuva said, bringing the service down.

The second was on the 746-mile (1,200km) cable between Helsinki and the German port of Rostock. It stopped working at about 2am GMT on Monday, according to the Finnish cybersecurity and telecoms company Cinia.

The same stretch of water is believed to have been targeted by several such suspected attacks, including the explosions along the Nord Stream gas pipelines in 2022.

The Finnish and German foreign ministers on Monday released a joint statement expressing their “deep concern” about the severed undersea cable between Finland and Germany, and said a “thorough investigation” was under way.

“The fact that such an incident immediately raises suspicions of intentional damage speaks volumes about the volatility of our times,” said the Finnish foreign minister, Elina Valtonen, and her German counterpart, Annalena Baerbock.

“Our European security is not only under threat from Russia’s war of aggression against Ukraine, but also from hybrid warfare by malicious actors. Safeguarding our shared critical infrastructure is vital to our security and the resilience of our societies.”

In a separate statement, Baerbock said Germany was also experiencing such issues, including cyber-attacks, surveillance of critical infrastructure and, referring to an incendiary device plot that caused fires at two DHL sites in Birmingham and Leipzig in July, “parcels suddenly exploding when transported on planes”. She added: “These can’t all just be coincidences.”

“The government is following the development of events very closely against the backdrop of a serious security situation and is in contact with the authorities. It is absolutely important to find out why there are currently two cables in the Baltic Sea that are not working.”

The Lithuanian navy has said it will intensify surveillance in the affected areas of the Baltic.