Swedish prosecutors announced Sunday night that they have opened a preliminary investigation into suspected aggravated “sabotage” and ordered the detention of a vessel in the Baltic Sea suspected of damaging an underwater fiber optic cable connecting Latvia and the Swedish island of Gotland earlier that day.

The Nordic country has opened an investigation into the damage, just weeks after NATO stepped up its military presence in the area following a series of similar incidents.

Swedish authorities seized the Vezhen, sailing under the flag of Malta and registered with a Bulgarian shipping company, on Sunday over suspected sabotage of an underwater cable.