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BERLIN (AP) — A ship chartered by the operator of the Nord Stream 1 natural gas pipeline has arrived at the site of last month’s explosions under the Baltic Sea to survey the damage, the company said Thursday.

Undersea explosions late last month ruptured Nord Stream 1, which until Russia cut off supplies at the end of August was its main supply route to Germany. They also damaged the Nord Stream 2 pipeline, which never entered service as Germany suspended its certification process shortly before Russia invaded Ukraine in February.

Investigators in Sweden, Denmark and Germany are looking into what happened. Danish officials last week confirmed that there had been “extensive damage” to the pipelines and that the cause of the damage was “powerful explosions.”

The leaks occurred in international waters but within the exclusive economic zones of Denmark and Sweden. Investigators haven’t yet given any information on who might have been responsible.

Nord Stream 1 operator Nord Stream AG, in which Russia’s Gazprom has a majority stake, said a specially equipped vessel has arrived at the location of the damage in Sweden’s exclusive economic zone. It said survey work on the damaged area is expected to take three to five days.

The Swiss-based company said it is still awaiting a Danish decision on permits for damage assessment in that country’s exclusive economic zone.

The Swedish Armed Forces confirmed to Swedish broadcaster SVT that a Russian ship was on site to carry out investigations for Nord Stream.

“We have known about their plans for some time,” said Jimmie Adamsson, the navy’s head of communications. “Since it is international water, no permission from the Swedish authorities is needed to carry out this type of investigation.”

Separately, the Swedish Navy said on Twitter that it was carrying out “supplementary bottom surveys” at the site of the gas leaks using minesweepers. It said that work was not part of the criminal investigation, but didn’t elaborate.