(Adds White House comment)
By David Ljunggren
OTTAWA, Jan 15 (Reuters) - Canada has postponed a summit with the leaders of the United States and Mexico, officials said on Thursday, amid persistent tensions over the construction of TransCanada Corp's Keystone XL pipeline and other issues.
Canadian Prime Minister Stephen Harper had been due to host U.S. President Barack Obama and Mexican President Enrique Pena Nieto for the annual meeting of the so-called Three Amigos, and a date had tentatively been set for late February, said two sources familiar with the plans.
Canadian officials recently reached out to Washington and Mexico City to say late February would not work, but gave no reasons, the sources said.
"It's my understanding that (the summit) ... has been postponed from early this year to later in the year," White House spokesman Josh Earnest said in Washington.
But Harper spokesman Jason MacDonald said no date had been formally announced.
"We intend to host the meeting later in the year," he said.
If Obama did come to Canada he would face pointed questions about the proposed Keystone XL pipeline, which would run from the Alberta oil sands to the United States.
Canada wants the project to go ahead and has expressed impatience that Washington is still mulling the fate of the pipeline after six years of study. Environmental activists are putting heavy pressure on Obama to veto Keystone XL.
Canadian Natural Resources Minister Greg Rickford told reporters on Wednesday that he still believed the pipeline would be approved one day - a strong hint that Canada is looking beyond Obama, who will leave office in early 2017.
Earnest said U.S. ties with Canada were far broader than the pipeline.
"As long as this meeting gets rescheduled in a timely fashion ... and we can continue to have the kind of strong relationship that we have with our neighbors to the north, then there's no concern here at the White House about it," he said.
Ottawa's relations with Mexico are also strained over Canadian rules that impose visas for visiting Mexicans.
Canada's official opposition New Democrats said the postponement showed that Harper could do little to move Keystone XL forward and wanted to avoid being pressured by Mexico over visas.
MacDonald dismissed the suggestion that Harper wanted to delay the summit because he planned to call a early snap election in March or April and catch opposition parties off guard. The next vote is scheduled for October. (Additional reporting by Jeff Mason in Washington; Editing by Jeffrey Benkoe and Christian Plumb)