Thousands of people have taken part in a huge clean-up operation to remove oil and tar from beaches along Brazil’s north-eastern coast.

Volunteers, as well as government workers, have been using wheelbarrows, spades and plastic gloves to remove the thick tar from the sand and water.

The source of the spill, which spans more than 1500 kilometres, remains a mystery seven weeks after it was first detected.

It spans more than 1,500 kilometres, and experts say this could be the worst disaster for the region’s coral reefs.

It has affected wildlife and popular beaches including Praia do Futuro in Ceará, Maragogi in Alagoas, and Itacaré and Ilhéus in Bahia.

At least 15 sea turtles, and two seabirds have been found dead, the environmental agency Ibama said.

It was not clear if the volume of oil was increasing or decreasing and how long the problem, which has affected 187 places in nine states, will last.

Oil deposits on Lagoa do Pau beach, in the northeast of Brazil.

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A man shows oil deposits from Lagoa do Pau beach, in the northeast of Brazil. Photo: AFP

On Thursday, Ibama President Eduardo Bim said tests had proved the crude oil was produced in Venezuela, but officials had not been able to identify the vessel responsible for the leak.

This did not mean that Venezuela was responsible for the leak, he added, describing the case as “unprecedented”.

Venezuela, however, has denied responsibility for the oil.

The incident is more challenging than a typical oil spill because the dense crude is not floating on the surface, and only appears when it washes up on shore, Mr Bim was quoted by Reuters news agency as saying.

Floating barriers usually employed to prevent oil from washing ashore have little effect, for example, so the work has been focused on cleaning up the crude as it comes to the coast.

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In Pernambuco state, 30 tonnes of oil were removed from beaches on Saturday alone.

Meanwhile, federal prosecutors have accused the federal government of failing to organise a response, saying the spill has caused environmental damage in an area spanning 2,100 kilometres.

-BBC