Finnish authorities said Wednesday they have opened an investigation into the rupture of a data cable under the Baltic Sea, adding to a Swedish probe into the possible sabotage of that link and another cable.

Germany and Finland say they are "deeply concerned" after an undersea cable linking the countries was severed. The rupture of the 1,170km (730-mile) telecommunications cable - which is being investigated - comes at a time of heightened tension with Russia.

Two undersea fibre-optic communications cables in the Baltic Sea, including one linking Finland and Germany, were severed, raising suspicions of sabotage by bad actors, countries and companies involved said on Monday.