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Environmental groups in the US have begun a legal challenge to President Donald Trump's approval of the controversial Keystone XL oil pipeline.

The 1,180-mile (1,900km) pipeline will carry tar sands oil from Canada to refineries on the Texas coast.

A lawsuit filed in Montana by a coalition of groups says more environmental scrutiny is required.

They - and some landowners - are concerned about potential contamination of ground and surface water.

Supporters of the project say such fears are exaggerated.

President Trump, who overturned President Barack Obama's rejection of the project, has said the pipeline will create jobs and improve US energy independence.

Keystone XL pipeline: Why is it so disputed?

The environmental groups - including the Sierra Club, Natural Resources Defense Council, Northern Plains Resource Council, Bold Alliance, Friends of the Earth and the Center for Biological Diversity - say an environmental review of the proposed pipeline that was completed in 2014 is inadequate and outdated.

Their lawsuit says that review minimises or ignores significant environmental impacts of Keystone XL, which will carry a particularly dirty type of crude oil, "including harm to land, air, water, and wildlife".

More jobs?

The $8bn pipeline, first proposed in 2008, would carry more than 800,000 barrels of oil a day.

TransCanada, a Calgary-based company, wants to build it to carry oil from Canada through Montana, South Dakota and Nebraska. From there, it would connect with an existing Keystone pipeline network that would transport the oil to Texas Gulf Coast refineries.

The US state department issued a permit for the project earlier this month after an evaluation which was required because the pipeline crosses an international border.

But regulators in Nebraska have still to review the proposed route through their state before approving or rejecting it.

The state's elected Public Service Commission will decide whether it believes the project serves a public interest, after reviewing evidence presented at a public hearing.

TransCanada says the pipeline will create 13,000 jobs over two years, but opponents argue the vast majority of these jobs will be short-term work in the construction phase.