The United States formally rejected Wednesday a request from the Canadian company that wants to build the Keystone XL pipeline for a pause in the US review process.

TransCanada made the request Monday, citing litigation pending in Nebraska over the route the pipe line would take in that state as oil flows from Canada's Alberta province down through the US to the Gulf of Mexico.

The State Department said Tuesday its years-long review of the whole project would continue, and on Wednesday made it official by telling TransCanada in writing.

"We have communicated our decision to continue our review and we've communicated to that to TransCanada, in writing, today," said department spokesman John Kirby.

"We're not required to pause it based on an applicant's request. There's no legal basis to do that," he added.

TransCanada has said a ruling in Nebraska would take seven to 12 months. A halt in the review would perhaps have delayed a decision on building the pipeline until after the US presidential election in November 2016.