Leaders from 11 Native American tribes stormed out of a meeting with US federal officials in Rapid City, South Dakota, to protest the proposed Keystone XL pipeline, which they say will lead to ‘environmental genocide.’

Native Americans are opposed to the 1,179-mile (1,897km) Keystone XL project - a system to transport tar sands oil from Canada and the northern United States to refineries in Texas - for various reasons, including potential irreversible damage to sacred sites, pollution, and water contamination.

Although the planned pipeline would not pass directly through any Native American reservation, tribes in proximity to the proposed system say it will violate their traditional lands and that the environmental risks of the project are simply too great.

Russ Girling, CEO of TransCanada, the company that hopes to build the pipeline, has promised in the past that Keystone XL will be “the safest pipeline ever built.”

The Indian groups, as well as other activist organizations, doubt the claim, saying the risks involved in the project are too high.

In an effort to ease their concerns, officials from the Department of State agreed to meet with tribal leaders on Thursday in the Hilton Garden Inn in Rapid City, Michigan.

Before the talks could begin, however, tribal leaders walked out, angered that the government had sent what they considered low-level representatives.

In a press conference following the walkout, tribal leaders took turns criticizing the project, as well as the Obama administration.

"I will only meet with President Obama," Bryan Brewer, president of the Oglala Sioux Tribe, told the Rapid City Journal.

Others mentioned environmental concerns with the proposed pipeline, which echo the concern of environmental groups across the country.

Casey Camp-Horinek, an elder with the Southern Ponca Tribe based in Oklahoma, compared the pipeline and other environmental damage to the historical events that had decimated her people during European colonization.

"We find ourselves victims of another form of genocide, and it's environmental genocide, and it's caused by the extractive industries," she said.

Charles LoneChief, vice president of the Pawnee Business Council, headquartered in Oklahoma, said the public was misinformed about the pipeline's environmental risks.

Unlike a traditional crude oil pipeline, Keystone XL will pump oil that is collected from tar sands. To turn this substance into a transportable liquid, oil companies must add chemicals that environmental groups warn are highly toxic.

"That gets into our waterways, our water tables, our aquifers, then we have problems," LoneChief said.

The US Environmental Protection Agency (EPA) has estimated that the Keystone XL pipeline will increase annual US carbon pollution emissions by up to 27.6 million metric tons – the impact of adding nearly 6 million cars on the road, according to the Environment News Service.

Robin LeBeau, a council representative for the Cheyenne River Sioux Tribe based in South Dakota, pledged to protest against any construction, even if that meant standing in front of bulldozers.

"What the State Department, what President Obama needs to hear from us, is that we are going to be taking direct action," she said.

I believe this is going to be one of the biggest battles we are ever going to have, LeBeau added.

This is not the first time that Native American groups have spoken out on the project.

Leaders from ten Canadian and US indigenous groups gathered in Ottawa, Ontario in March to protest the construction of pipelines.

“Tar sands pipelines will not pass through [our] collective territories under any conditions or circumstances,” the tribes said at a press conference.