The Swedish coastguard has reportedly found a fourth leak on the Nord Stream gas pipeline.
Swedish newspaper Svenska Dagbladet quoted the coastguard as saying it had located the leak after two pipelines running from Russia to Germany were damaged in three places on Monday.
“Two of these four are in Sweden’s exclusive economic zone,” coastguard spokesperson Jenny Larsson told the newspaper.
The two other holes are in the Danish economic zone.
The suspected acts of sabotage in the Baltic Sea were likely premeditated attacks using underwater explosives detonated remotely, a British defence source told Sky News.
They said the mines could have been lowered on a long line, dropped over a boat or placed next to the pipelines with an underwater drone months or even years ago.
The European Union also believes the leaks are a result of sabotage. Russia has said accusations it is responsible are “predictable” and “stupid”.
The Nord Stream 2 line runs 764 miles (1,230km) from Russia to Germany and had been due to carry gas to Europe until Russia invaded Ukraine and Germany refused to grant its operators a licence, leaving it mothballed.
Gas bubbles in the sea off the coast of the Danish island of Bornholm. Pic: AP
The location of the first three leaks
Gas has spewed into the Baltic Sea since the first leaks were detected early on Monday morning about 14 miles (23km) southeast of Denmark’s Bornholm Island.
Sweden’s national seismology centre previously said stations recorded “powerful subsea blasts” in the area the leaks occurred.
Bjorn Lund, a seismologist with Uppsala University, told national broadcaster SVT: “There is no doubt that these were explosions.”