Brazilian investigators said on Friday a Greek-flagged ship carrying Venezuelan crude was the source of oil tarring thousands of kilometres of coastline over the past two months.

While prosecutors and police did not name the vessel, a prosecutors’ document identified the ship as the Bouboulina, owned by Greece’s Delta Tankers Ltd. Police said the tanker appears to have spilled the crude about 700km (420 miles) off Brazil’s coast between July 28th-29th, bound for Singapore with oil loaded at Venezuela’s San Jose terminal.

Delta Tankers did not immediately respond to a request for comment.

Brazil’s solicitor general said the country would seek damages in the case, which has stained tropical beaches along 2,500km of coastline with a thick sludge, hurting tourism and fishing communities in the poorer northeast region.

“There is strong evidence that the company, the captain and the vessel’s crew failed to communicate authorities about the oil spill/release of the crude oil in the Atlantic Ocean,” said Brazilian prosecutors.

Federal police also executed warrants at the Rio de Janeiro addresses of Lachmann and Witt O’Briens, a subsidiary of Seacor Holdings, according to the document.

Neither maritime services company is suspected of criminal activity, although they both have commercial relationships with the Greek firm in question, said police, without naming any of the firms.

Volunteers help to clean up the oil sludge at the Itapuama beach, in Cabo de San Agostinho, Brazil. Photograph: EPA

Neither company responded immediately to requests for comment.

Brazilian authorities said they had also requested co-operation from international agencies, including Interpol, to further investigate the ship, its crew and the company.

Federal prosecutors said Brazil’s navy also had information regarding a prior detention of the vessel in the United States for four days due to “incorrect operating procedures related to the separation of oil and water for release in the sea”.

Nine states, 94 cities

It was unclear when the US detention occurred.

The police said oceanographic and geolocation data showed that the Greek ship was the only one navigating near the origin of the spill between July 28th and 29th, after docking in Venezuela about July 15th.

From late August to the end of October, the oil had washed ashore on nine states and 94 cities, according to federal police, killing scores of animals and closing hundreds of beaches.

Brazil has so far collected some 2,000 tonnes of sludge from its beaches in continuing clean-up efforts, while working to rehabilitate birds and sea turtles coated in the thick crude.

The slow and patchwork clean-up efforts, along with weeks of confusion about the cause of the spill have spurred criticism of the Brazilian government’s response. Officials have said Brazil is following standard protocols since the start of the disaster.

Because the heavy crude does not float on the ocean surface like most oil slicks, officials said traditional methods of tracking it and keeping it off the shore have been ineffective. – Reuters