Oscar-winning US actress and political activist Jane Fonda implored President-elect Donald Trump on Wednesday to get behind native Americans protesting over a controversial oil pipeline.

The actress spoke out as she closed her account at the Hollywood branch of Wells Fargo in protest at the bank's investment in the Dakota Access Pipeline, the subject of a months-long protest by indigenous tribes.

Asked by AFP what message she wanted to give the incoming president -- who reportedly owns a stake in the pipeline's operator Energy Transfer Partners -- she called on him to "honor the treaties that we have with the indigenous people."

"We are guests on their land and we have never treated that reality with enough seriousness," said the "Barbarella" star and fitness guru, who was celebrating her 79th birthday.

"They've been telling us for centuries how to live in relation to the land and we haven't paid attention, and now we're reaping what we've sown and it's about time we started listening."

Fonda had called a somewhat unusual news conference in a dry cleaner's behind the bank, cutting a birthday cake decorated with lettering spelling "Bankarella" in tribute to her role in first husband Roger Vadim's 1968 erotic sci-fi romp.

"They've never been asked to do a full environmental impact statement which is unthinkable given the amount of territory and water that they could damage," she told reporters.

"I just don't want to be involved in a bank that has done such poor due diligence to have invested in a company that's as bad as this."

The Standing Rock Sioux Tribe is concerned about potential water pollution and says the pipeline's route endangers areas with sacred historic artifacts. 

The conflict between the Sioux and pipeline operators has galvanized North American native tribes and supporters, who have camped out in their thousands near the construction site, some since April. 

The standoff has prompted violent clashes with law enforcement, as well as sympathetic protests nationwide. 

The movement won a victory earlier this month when the army refused the project a permit to bury the pipeline under the Missouri River, the source of drinking water for the Sioux. 

But the decision could be reversed when Trump takes over the White House in January, and his transition spokesman said Monday the incoming administration was supportive of the 1,172-mile (1,886-kilometer) oil pipeline, which would snake through four US states. 

Wells Fargo reportedly has $120 million in a $2.5 billion credit agreement alongside 16 other financial institutions funding the project.

It told AFP it had invested $52 billion in environmentally sustainable businesses since 2012 and its various projects had produced 10 percent of all solar panel and wind energy generated in the US over the last year. 

"As a company committed to environmental sustainability and human rights, we respect all the differing opinions being expressed in this dispute, and hope all parties involved will work together to reach a peaceful resolution," a spokesman said.