New Delhi, April 1 -- Environmentalist groups accused Mexico's government of lying about the origins of a massive oil spill in the Gulf of Mexico, something authorities promptly denied.

The spill of off the coast of the southern Veracruz state has spread more than 373 miles and into seven nature reserves. It has dealt an environmental blow to the region as turtles and other marine life have been found on sea shores coated in oil, and to fishermen who have been unable to work in the oceans they have fished for decades.

Mexico's government reported that 800 tons of hydrocarbon-laden waste have spilled into the ocean. The government said the spill started in March and the sources were a ship anchored off the coastal state of Veracruz and t...