Investigators are trying to unravel the mystery of how two undersea internet cables in the Baltic Sea were cut within hours of each other, with European officials saying they believe the outage was an act of sabotage and US officials suggesting it was likely an accident .

The two cables – BCS East-West connecting Lithuania and Sweden and C-Lion1 connecting Finland to Germany – were suddenly cut on Sunday and Monday.

European leaders were quick to voice their suspicions. German Defense Minister Boris Pistorius said that “no one believes that these cables were accidentally cut”.

The foreign ministers of Finland and Germany said in a joint statement that they were “deeply concerned” by the incident and raised the possibility that it was part of a “hybrid war”, specifically mentioning Russia in their statement.

Their assessment was not made out of thin air. Russia has been accused of waging a hybrid war against Europe after a string of suspicious incidents, arson attacks, explosions and other acts of sabotage in several European countries were traced to Moscow.

And the cable cut came just weeks after the US warned that Moscow could target critical undersea infrastructure. This followed months of suspicious movements of Russian vessels in European waters and the significant strengthening of a dedicated secret Russian maritime unit tasked with seabed surveillance.

But two US officials familiar with the initial assessment of the incident told CNN on Tuesday that the damage is not believed to be deliberate activity by Russia or any other nation.

Instead, the two officials told CNN they believed it was likely caused by an anchor being dragged by a passing ship. Such accidents have happened in the past, though not in quick succession like the two on Sunday and Monday.

The Kremlin on Wednesday rejected “laughable” suggestions that it was involved, saying it was “absurd to keep blaming Russia for anything without any basis”.

However, law enforcement agencies in both Sweden and Finland have indicated that they believe the damage is deliberate.

The Swedish prosecutor’s office announced on Tuesday that it had launched a preliminary investigation into alleged sabotage. Then on Wednesday, Finland’s National Bureau of Investigation announced it was opening a criminal investigation into the suspected offenses of aggravated criminal mischief and aggravated interference with communications.

One vessel in particular has piqued the interest of authorities and online sleuths.

The Chinese-flagged vessel Yi Peng 3 was spotted in the area around the time the two cables were cut. The bulk carrier was sailing from the Russian port of Ust-Luga, where it docked for several days.

On Wednesday, Danish armed forces said they were present in the area near the Yi Peng 3, but did not say whether they had pursued the vessel.

Asked about the ship during a press briefing on Wednesday, Chinese Foreign Ministry spokesman Lin Jian said he was “not aware of the situation”.

He said China has “always fully fulfilled its flag state obligations and requires Chinese ships to strictly comply with relevant laws and regulations.”

“We also attach great importance to the security protection of submarine infrastructure and work with the international community to actively promote the construction and protection of submarine cables and other global information infrastructure,” he said.

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