Nordic and Baltic seismologists said that they had detected blast-like waves on 8 October when a Baltic Sea gas pipeline ruptured but that the data was not strong enough to determine whether explosives were involved.
Authorities in Finland and Estonia, whose state-run companies own and operate the Balticconnector pipeline, have said that the damage appeared to be caused by "mechanical force" and that it may have been a deliberate act.
Norwegian seismology institute NORSAR, analyzing data collected in Finland, said it identified "a probable explosion" near the pipeline on Sunday at 0120 EET (2220 GMT Saturday), matching operator Gasgrid's statement that pressure fell before 0200 EET.
Waves measured after explosions tend to leave different signals to those sent out by earthquakes, the seismologists said.
"We know that it wasn't an earthquake, and we know there was an explosion, but what actually caused the explosion is something to be further investigated," NORSAR CEO Anne Strommen Lycke told Reuters.
"We have seen that there is speculation about whether some ship could have dragged the pipeline and that (this) caused a hole and then a subsequent explosion (but) that is too early to tell," she said.
Finland's National Bureau of Investigation said that external marks were found on the seabed beside the pipeline and that it was reviewing the movements of vessels and that anchor damage was a potential explanation.
The agency said mechanical damage and not an explosion looked like the most likely cause of the incident but a blast had not been ruled out.