Washington, Oct. 3 -- US President Donald Trump has cautioned South Korea that the cost could rise if it fails to commit to the Alaska pipeline project in the near term, after learning that Seoul continues studying the proposal.

At first, Trump signalled he would accept a decision by South Korea not to join. His tone changed once a reporter informed him that the country had yet to give formal approval.

"Tell 'em if they don't sign shortly, I'm going to double it up. Okay?" Trump told reporters at the White House before boarding Marine One.

The exchange opened when a journalist raised South Korea's current position on the Alaska pipeline project.

"South Korea said they have not signed off on this Alaska pipeline yet. They're still stud...