Indigenous communities that sued Occidental Petroleum over contamination in Peru's northern Amazon have reached an out-of-court settlement in which the California-based oil company will pay them an undisclosed sum.

The amount is confidential, under a settlement that was reached in 2013 in Los Angeles federal court but not announced until Thursday. The money is to fund community development projects.

The case was the first of its kind involving oil drilling in South America to advance in U.S. courts, said attorney Marco Simons of EarthRights International , which represented the plaintiffs.

Five Achuar communities, along with the environmental group Amazon Watch, sued Occidental in 2007, alleging the company spilled oil and dumped toxic byproducts in their territory over three decades ending in 2001, causing premature deaths, birth defects and other health problems.

Simons said the pollution caused "death, generalized contamination and destruction of the Achuar way of life." The Achuar are traditional hunters and gatherers whose diet depends highly on river fish.

Amazon Watch says a report it issued in 2007 found elevated levels of lead and cadmium in Achuar children's blood.

The case was initially dismissed in 2008, with the lower-court judge ruling it should be heard in Peru instead. The plaintiffs successfully appealed, however, and the U.S. Supreme Court let the 9th Circuit Court's decision stand.

An Achuar leader, Adolfina Garcia, told reporters on Thursday that the group could not have received a fair trial in Peru.

"We don't have any faith in Peru. There is a lot of corruption," she said.

There was no immediate comment from Occidental, which requested that an email inquiry be sent.

The contamination occurred in the Corrientes river basin near Ecuador in a lot spanning more than 1 million acres (400,000 hectares) of virgin rainforest where Occidental drilled more than 150 wells after signing a 1971 contract with Peru's government, according to EarthRights International.

In 2001, Occidental turned over the operation to Argentina's Pluspetrol, which in 2012 and 2013 were fined a total of $17 million for contaminating the region.

Peru's government declared an emergency in 2013 over the contamination but local Achuar communities complain that the government has done nothing to clean up the contamination.

They have mounted protests in recent weeks, occupying Pluspetrol facilities.

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Associated Press writer Frank Bajak contributed to this report.