The Russian-controlled operator of the ruptured Nord Stream 1 gas pipeline says it has received all necessary permissions from various authorities and agencies in Denmark to proceed with a planned survey of a second site on the damaged subsea pipeline which runs from Russia across the Baltic Sea to Germany.

Danish police have stated that “powerful explosions” blew four holes in Nord Stream 1 and the newer Nord Stream 2 when the massive leaks occurred in September.

Registered in Switzerland, the Nord Stream consortium said the Danish Maritime Authority had granted the operator an exemption that allows an approach to the damaged area.

On receiving the permissions a vessel, chartered by Nord Stream, moved into the area of damage and began to survey the pipeline rupture points, the statement added.

Although Nord Stream has refused to reveal the name of the offshore support ship performing the survey, marine traffic services have identified it as Nefrit, a vessel that was operated by a Norwegian company until last year but which was reportedly purchased by a privately held contractor based in Saint Petersburg.

“The duration of the survey will depend on access restrictions to the damaged area related to weather conditions”, Nord Stream stated.

Earlier this month, Nord Stream released a statement claiming to have found unnatural craters after Nefrit had completed the underwater inspection of damage to the Nord Stream 1 pipeline in the Swedish maritime zone.

However, the operator provided no visual evidence of the craters, in contrast to that presented after a subsea survey was carried out by a remotely operated vehicle organised by a Swedish newspaper.

Authorities in Denmark, Sweden and Germany had earlier described three ruptures detected on the Nord Stream 1 and Nord Stream 2 pipelines as acts of sabotage as the damage had been caused by explosives after authorities in these countries had completed their own site surveys.

Russian officials initially blamed the US but later accused the UK’s Royal Navy — charges that the UK has denied.

Nord Stream has yet to reply to several enquiries from Upstream on whether it has plans to direct Nefrit to a third site, located to the southeast of Bornholm Island where the first subsea line of Nord Stream 2 was damaged.

German regulatory concerns prevented Nord Stream 2 from going into service after being commissioned last year, and the pipeline was then caught up in European sanctions and the Russian response to them.

Law enforcement and intelligence agencies in Denmark, Sweden and Germany are continuing their inquiries into what caused the ruptures in September, and the resulting rush of pressurised gas that continued escaping to the sea surface for a week after the incident.

‘Dark ships’

Speculation about the cause of the ruptures was fuelled again last week after a private satellite company said that it detected the presence of two unknown vessels in the vicinity of the damaged areas several days before the explosions.

After looking at various satellite images days before the incident, Prague-based SpaceKnow identified two “dark ships”, each measuring around 95 to 130 metres in length that passed within several kilometres of where Nord Stream 2 was leaking.

Once SpaceKnow had identified the ships it reported its findings to officials at Nato, the company tweeted.

SpaceKnow chief executive officer Jerry Javornicky was last week quoted by technology publication Wired as saying that the vessels had their identification beacons turned off.