(Adds comment from Canadian prime minister's office, paragraphs 4-5)
By Valerie Volcovici and Mike De Souza
WASHINGTON/OTTAWA, April 2 (Reuters) - Canada declined a U.S. invitation last week to jointly announce climate policy cooperation with Mexico, with Ottawa saying it has not yet finalized its own domestic strategy, sources from both countries familiar with the discussions said on Thursday.
On March 24, three days before the United States and Mexico announced they would partner on a high-level bilateral clean energy and climate policy task force, U.S. officials approached Canadian counterparts asking them to join the effort, three sources said.
One source said that, while Canadian officials said they were supportive of North American harmonization of climate policy, they were not yet prepared to join the continental partners.
A spokesman for Prime Minister Stephen Harper said the suggestion that Canada declined to participate was incorrect.
"This was an initiative between Mexico and the U.S. Canada fully supports continental action and looks forward to continuing to work with both the U.S. and Mexico on reducing greenhouse gas emissions," the spokesman said.
Shane Buckingham, spokesman for Canadian Environment Minister Leona Aglukkaq, had earlier said Ottawa was preparing to submit its climate plan to the United Nations "in the weeks ahead" after it gets feedback from the provinces about their own emissions-cutting policies.
"Given the importance of this submission, Canada wants to ensure it has the most complete picture of provincial and territorial plans possible before submitting," Buckingham said.
On March 27, Mexico said it would cap its greenhouse gas emissions by 2026, becoming the first emerging economy to submit its climate plan ahead of a key U.N. summit in Paris from Nov. 30 to Dec. 11.
The United States formally submitted on Tuesday its own climate plan, which commits the country to reduce greenhouse gas emissions up to 28 percent by 2025 below 2005 levels.
Buckingham said the United States and Canada already align regulatory initiatives, including harmonizing vehicle standards, reducing sulfur in gasoline and phasing down HFCs.
He said Canada also works jointly with the United States and Mexico through the Commission for Environmental Cooperation.
In December, Harper said in a televised interview with the CBC that his government preferred a continental response to climate change rather than imposing a unilateral price on carbon on Canada's oil sector, its fastest growing source of greenhouse gas emissions.
Harper's conservative government opposes carbon pricing policies, which have support from opposition parties.
The environment critic for the opposition New Democratic Party in the Canadian Parliament said climate policy was not a priority for the Harper government.
"They're hoping to form some kind of Axis of Denial with the next Republican (U.S.) government and they're utterly disengaged on the climate file," said Megan Leslie, deputy leader of the NDP. (With additional reporting by David Ljunggren and Jeffrey Hodgson; Editing by David Gregorio and Paul Tait)