Spain launched an investigation on Thursday into the sinking of a Russian ship off the Canary Islands, as coastguards battled a six-km (3.7-mile) oil slick close to tourist beaches.
Environmentalist group Greenpeace criticised authorities for towing the burning fishing vessel out to sea after it caught fire in Las Palmas port early on Sunday.
The Oleg Naydenov, carrying 1,409 tonnes of fuel oil, sank late on Tuesday 15 nautical miles south of Gran Canaria. Television images on Thursday showed oil floating on the water.
Spain has sent three tugboats and two light aircraft to control the leak, Public Works Minister Ana Pastor told reporters. Experts were trying to locate a robot which could dive 2.4 kilometres deep to inspect the wreck.
The state prosecutor for the Canary Islands has started an investigation into the circumstances surrounding the sinking, a government spokesman said. The waters to the south of the islands are populated by turtles and dolphins.
The accident stirred memories of Spain's worst environmental disaster when the Prestige oil tanker sank off the northwestern coast of Spain in 2002.
The Prestige was carrying over 50 times more oil than the Oleg Naydenov, but Greenpeace said the Russian ship nevertheless posed a significant threat.
"The hull and tanks of a ship in such bad condition could already be breaking up under the kind of pressure found at such depths," the group said in a statement.
Oil spills can be harder to contain in the open sea and environmentalists recommend damaged ships are dealt with in ports or bays.
The World Wildlife Fund said the area where the ship had sunk had deep-sea coral and a significant population of bottle-nosed dolphins.
(Reporting by Sonya Dowsett; editing by Andrew Roche)