Accident or sabotage? Investigators are trying to unravel the mystery of how two undersea telecommunications cables in the Baltic Sea were cut within hours of each other, with European officials saying they believe the outage was sabotage and U.S. officials saying it may have been accident.

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

European leaders were quick to voice their suspicions. German Defense Minister Boris Pistorius insisted 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” about the incident, noting that there was a possibility that it was part of a “hybrid war,” specifically mentioning Russia in their statement.

Their evaluation is not in a vacuum. Russia has been accused of waging a hybrid war against Europe following a series of suspicious incidents, arson attacks, explosions and other acts of sabotage in several European countries traced to Moscow.

And the issue of the cut cables came just weeks after the US warned that Moscow was likely to target critical undersea infrastructure. This followed months of suspicious movements of Russian vessels in European waters and the significant reinforcement of a special Russian secret maritime unit tasked with surveying the seabed.

However, two US officials with knowledge of the initial assessment of the incident told CNN on Tuesday that they do not believe the damage was intentional activity by Russia or any other nation.

Instead, the two officials told CNN they believed the cables were cut most likely by an anchor being dragged by a passing vessel. Such accidents have happened in the past, although not in quick succession like the two on Sunday and Monday.

The Kremlin on Wednesday rejected what it called “ridiculous” reports that it was involved, saying it was “absurd to keep blaming Russia for anything without any reason.”

However, authorities in both Sweden and Finland said they believe the damage was intentional.

Sweden’s public prosecutor’s office announced on Tuesday that it had opened a preliminary investigation into sabotage. Then on Wednesday, Finland’s National Bureau of Investigation announced it had opened a criminal investigation into the matter.

One vessel in particular has piqued the interest of the authorities and internet “greyhounds”.

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 had been moored for several days.

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

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

It added that China has “always fully fulfilled its obligations as a flag state and requires Chinese ships to strictly abide by relevant laws and regulations.”

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