A senior Canadian official on Wednesday warned against a US rejection of the massive Keystone XL pipeline, saying it would be a "serious reversal" in the neighbors' energy relationship.

"It is a certainty that pipelines will continue to be built in the United States regardless of the approval or the rejection of Keystone XL," Canada's natural resources minister Joe Oliver told a Washington think tank.

"Rejecting this project would represent a serious reversal in our long-standing energy relationship," he added, at a conference held by the Center for Strategic and International Studies (CSIS).

The United States is expected to decide soon on the fate of TransCanada's $5.3 billion proposal to build a 1,179-mile (1,897-kilometer) pipeline from the Canadian province of Alberta to the US state of Nebraska, where it would hook up with a new southern leg to bring the oil to refineries in Texas.

Pipeline supporters say the project would generate much-needed jobs for the sluggish US economy, while opponents warn it could have a dire impact on the environment and vital groundwater resources.

"Ultimately, this comes down to a choice: the US can choose Canada, a friend, neighbor and ally, as a source of its oil imports, or it can choose to continue to import oil from less friendly, less stable countries with weaker or perhaps no environmental standards," Oliver said.

He went on to describe several state-of-the-art protection measures built into the pipeline project as well as a thorough inspection regime, saying: "This is not your grandfather's pipeline."

The State Department is expected to make a final recommendation on the project to President Barack Obama in the coming months.