US imports of crude oil from the Amazon are driving the destruction of some of the rainforest ecosystem’s most pristine areas and releasing copious amounts of greenhouse gases, according to a new report.

The study, conducted by environmental group Amazon Watch, found that American refineries processed 230,293 barrels of Amazon crude oil a day last year.

And California, despite its green reputation, refines an average of 170,978 barrels, or 7.2m gallons, of Amazon crude a day, with the Chevron facility in El Segundo accounting for 24% of the US total alone.

The expansion of planned oil drilling poses “one of the most serious threats” to the western region of the Amazon, with most of the oil originating from Ecuador, Peru and Colombia. While green groups have enjoyed some success in fighting the Amazon ambitions of large oil firms like Chevron, other players from countries such as China have moved in, with proposed oil and gas fields now covering 283,172 sq miles of the Amazon – an area larger than Texas.

Felling the carbon-rich trees of the Amazon produces greenhouse gases even before the oil is transported and burned, while indigenous communities and the Amazon’s vast trove of biodiversity are also at risk.

Ecuador’s state oil company PetroAmazonas recently started drilling close to the Yasuni national park, which is considered to be one of the most biologically rich places on Earth. The park contains 655 endemic tree species – more than the US and Canada combined – as well as two of the last tribes in the world living in voluntary isolation.

As oil interests seek to exploit areas of the Amazon, there are fears that indigenous communities will suffer from pollution, displacement and deadly illnesses due to a lack of acquired immunity.

“Our demand for Amazon crude is literally driving the expansion of the Amazon oil frontier and is putting millions of acres of indigenous territory and pristine rainforest on the chopping block, ” said Leila Salazar-López, executive director of Amazon Watch.

“Breaking free from oil dependence and keeping remaining fossil fuels in the ground is an urgent, collective endeavor, and the life-giving Amazon rainforest must be one of the first places we start.”

After crude is refined in California and elsewhere it is distributed as diesel to vehicle fleets across the US. Adam Zuckerman, a California-based campaigner for Amazon Watch, said “virtually every company, city and university in California and around the country contributes to the destruction of the Amazon rainforest.”

California has burnished its environmental reputation with lofty goals to cut greenhouse gas emissions, boost energy efficiency and slash petroleum use in cars and trucks.

Despite this, the state is dependent upon oil imports from countries such as Ecuador, in part because of clean energy policies that discriminate against the heavy grade oil produced by countries such as Canada. Meanwhile, an explosion at the ExxonMobil refinery in Torrance, California, in February 2015 caused the state to increase its gasoline imports to more than 10 times the typical level.

Zuckerman said Amazon Watch wants California to consider human rights issues when it imports oil, as well as for “no go zones” such as the Amazon basin to be established in decision making. Around 40 US businesses that use Amazon crude oil have been contacted by the NGO over the issue.

A spokesman for California governor Jerry Brown did not answer whether new laws were being considered to reduce Amazon crude imports but said the administration has taken “nation-leading action to fight climate change, decarbonize our economy and end our dangerous addiction to foreign oil”.

A spokesman for the Western States Petroleum Association, which represents refineries in California, said the group did not wish to comment.