PIERRE (AP) - The Keystone XL oil pipeline developer said in a letter this week to a Native American tribal chairman that the company will start moving materials and preparing construction sites for the project in Montana and South Dakota.

TransCanada Corp. said in the letter to Cheyenne River Sioux Chairman Harold Frazier, of South Dakota, that the work would start in July and go through the fall. The chairman on Thursday tweeted copies of TransCanada's message and his response on the tribe's letterhead: "We will be waiting."

Frazier wasn't immediately available on Friday to comment to The Associated Press. Keystone XL faces intense resistance from environmental groups, Native American tribes and some landowners along the route.

The project would cost an estimated $8 billion. The 1,179-mile pipeline would transport up to 830,000 barrels a day of Canadian crude through Montana and South Dakota to Nebraska, where it would connect with lines to carry oil to Gulf Coast refineries.

TransCanada spokesman Terry Cunha said in an email that the preparatory work will ramp up over the year to position TransCanada for construction in 2019. He said it would include moving pipe and equipment to start clearing activities to prepare for getting final permits and approvals for construction.

But the project faces legal hurdles. Nebraska landowners have filed a lawsuit challenging the Nebraska Public Service Commission's decision to approve a route through the state.

A separate federal lawsuit brought by Montana landowners and environmental groups seeks to overturn President Donald Trump's decision to grant a presidential permit for the project, which was necessary because it would cross the U.S.-Canadian border.

South Dakota's Supreme Court in June dismissed an appeal from pipeline opponents - including the Cheyenne River Sioux - of a judge's decision last year upholding regulators' approval for the pipeline to cross the state.