It is unclear whether those ships had anything to do with the leaks, which are believed to have been caused by underwater explosions, but it's one of the many factors that investigators will be looking into, two Western intelligence officials and one other source familiar with the matter said, according to CNN.
Russian submarines were also observed not far from those areas last week, one of the intelligence officials said, as cited by CNN.
The US broadcaster quoted a Danish military official as saying that Russian ships routinely operate in the area and the presence of the ships does not necessarily indicate that Russia caused the damage.
"We see them every week,” the Danish military official said, according to CNN. “Russian activities in the Baltic Sea have increased in recent years. They’re quite often testing our awareness – both at sea and in the air.”
But the sightings on Monday and Tuesday cast further suspicion on Russia as the only player in the region believed to be capable of and motivated to deliberately damage the pipelines, CNN said on its website.
US State Department spokesman Ned Price on Wednesday dismissed suggestions that the United States damaged the Russia-Germany pipelines, calling such claims “preposterous” and part of "Russian disinformation."
He told reporters that Washington was “helping with the investigation” into the Nord Stream leaks.
Meanwhile, Poland’s Foreign Minister Zbigniew Rau said in Washington on Wednesday that Russia may have damaged the pipelines “to deepen European divisions over how to ensure energy security.”
Rau told public broadcaster Polish Radio: “... when we analyse the energy-security situation in the Baltic Sea region, the hypothesis that Russian services were behind the leaks is looking increasingly plausible.”
Sweden’s Svenska Dagbladet newspaper reported on Thursday that the Swedish Coast Guard had discovered a new leak from the pipelines, bringing the total number of gas leaks to four, according to the Reuters news agency.
Source: PAP, tysol.pl, CNN