Prime Minister Stephen Harper on Tuesday denied the top official in his office leaked a memo of a meeting between an aide to Barack Obama and a Canadian diplomat over the Democratic presidential hopeful's NAFTA position.

The controversy has dominated headlines ahead of Tuesday's crucial four-state vote and given Senator Hillary Rodham Clinton fresh ammunition to criticize her Democratic rival amid a rancorous campaign for the party's presidential nomination.

Prime Minister Stephen Harper called the leak of a memo describing a meeting between a Barack Obama aide and a Canadian diplomat over the Democratic presidential hopeful's NAFTA position 'regrettable.'
(Fred Chartrand/Canadian Press)

The media storm began late last week after someone told Canadian and American news outlets that Obama advisers had tipped off Canadian diplomats that their promise to reopen NAFTA was just empty talk aimed at winning votes in Ohio.

After Obama and the Canadian government denied the allegation, someone leaked a diplomatic memo describing such a conversation between Obama's economic adviser Austan Goolsbee and Consul General Georges Rioux.

The memo, written by a consular employee, says Goolsbee privately told Rioux that Obama's attack on free trade is "more reflective of political manoeuvring than policy."

An ABC News report identified Harper’s chief of staff, Ian Brodie, as the source of the details of a meeting to reporters.

The prime minister said his government is trying to find the person responsible for leaking the memo.

"It was not my chief of staff," Harper said during question period while under fire from NDP Leader Jack Layton, who demanded Brodie be fired if it is confirmed he tipped off reporters to the details of the meeting.

"The leak of this particular document is not only regrettable, as the Canadian Embassy in the United States has already said, it is completely unacceptable to this government and we will do our best to find out who did it."

But the prime minister spoke only of the leaked document and did not address specifically who told reporters of the meeting.

Layton accused Harper himself of "interference," alleging the prime minister personally authorized the leak in order to discredit the Obama camp and aid the Republicans, a charge Harper vehemently denied.

"The reality is what we're talking about here is a report that someone in the consulate to Chicago wrote to their superior," Harper responded. "There are literally thousands of documents like this written around the world by Canadian officials. It's ridiculous to think that the prime minister's office even ever sees these documents."

Tories using government to do 'dirty work': Rae

Democratic presidential hopeful Barack Obama's campaign has faced tough questions over a leaked Canadian memo that says his position on reopening NAFTA was 'more reflective of political manoeuvring than policy.'
(Rick Bowmer/Associated Press)

Liberal foreign affairs critic Bob Rae said it was clear the Tories are trying to help Republican friends at the expense of Canadian interests.

"They will do what is necessary to help Republicans. They're a nasty, unprincipled bunch, who are incompetent to boot," Rae wrote in a blog.

The controversy could play to the Republicans' advantage in November and hurt the Illinois senator in Ohio, a potential swing state where job losses have made the 15-year-old free-trade deal highly unpopular.

Obama and Clinton have both said they want to reopen the free-trade deal between Canada, the U.S. and Mexico to ensure better environmental and labour standards.

Trade Minister David Emerson and Finance Minister Jim Flaherty said U.S. officials should not forget the benefits of the agreement and hinted Canada could respond to a NAFTA pullout by renegotiating U.S. access to Canada's oil. With files from the Canadian Press