Several electricity and communications infrastructures have been damaged in the Baltic Sea in recent months, after Finland and Sweden, which border the Baltic, joined NATO.

Many experts and political leaders have attributed the incidents to a "hybrid war" carried out by Russia against Western countries.

Authorities in Gotland, off Sweden's southeastern coast, "received an alarm regarding a water pump" on Sunday at around 5:30 pm (1630 GMT), police told AFP in an email.

Police did not disclose the exact location of the incident.

"A technician was dispatched to the scene and discovered that someone had opened an electrical cabinet, disconnected a cable and thereby cut power to the pump," police said.

The technician reconnected the cable and reset the alarm at 9:30 pm.

"The pump is operational again," police said.

Gotland police have cordoned off the area around the electrical cabinet in order to carry out a crime scene investigation.

No suspect has been arrested yet, they said.

If the action had gone undetected, much of Gotland's water supply could have been interrupted.

Some 61,000 people live on the 3,140-square-kilometre (1,212-square-mile) island.

The pump "supplies large parts of Gotland," Susanne Bjergegaard-Pettersson, the head of the island's water supply and sewage operations, told the Aftonbladet daily.