A total of 24 sea turtles have been found dead on the beaches of the southern Mexican state of Oaxaca after oil spilled from a sunken loading buoy owned by state oil monopoly Petroleos Mexicanos, or Pemex, the environmental group Wildcoast/Costa Salvaje said.

Some 53,000 olive ridley sea turtles have arrived on Mexico's coasts in the past two days to nest on Morro Ayuta beach, which has been "polluted with oil residue," the environmental group said.

The loading buoy (an installation used to load crude oil on to tanker ships at sea) sank at a spot off the Oaxacan coast facing the Salina Cruz refinery, causing crude to spill onto six beaches in that state.

Since then, several grassroots organizations, including Costa Salvaje, have denounced environmental damage and economic harm to local fishermen.

An inspection of that area revealed "solidified petroleum residue" on numerous beaches - including Morro Ayuta, which draws massive numbers of nesting turtles, the environmental group said.

Last week, personnel with the federal prosecutor's office for environmental protection, or Profepa, registered 13 dead sea turtles with oil on their shells or skin, "bringing to 24 the number of sea turtles found dead on hydrocarbon-polluted beaches," the environmental group said.

Costa Salvaje demanded that Pemex "assume its responsibility for the environmental damage caused by the spill of 18,000 liters (4,750 gallons) of oil" and coordinate clean-up actions in coastal communities in compliance with "all necessary health and safety measures."

For its part, the National Human Rights Commission, Mexico's equivalent of an ombud's office, said Tuesday it has opened an "ex-officio" inquiry into the oil spill.

Environmental officials have given Pemex 48 hours to clean up the crude spilled on the beaches of Salina Cruz and instructed Profepa to ensure the company complies with the order. 

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