TORONTO — Canadian government investigators looking into the NAFTA leak controversy involving presidential candidates Hillary Rodham Clinton and Barack Obama said Friday that two top Canadian officials didn't leak confidential information.

In March, a 1,300-word document obtained by The Associated Press said Obama's senior economic adviser, Austan Goolsbee, told Canadian officials in Chicago that the debate over free trade in the Democratic presidential campaign was "political positioning."

Goolsbee later said his comments were misinterpreted, and Obama denied offering the Canadians any such ideas.

Prime Minister Stephen Harper appointed Canada's top civil servant, Kevin Lynch, to look into the leak of the document. Reports at the time pointed to Ian Brodie, Harper's top adviser, and Michael Wilson, Canada's ambassador in Washington, as possible sources of the leak.

Lynch hired two private investigators, but they could not finger the source of the leaks. But they did say Brodie or Wilson didn't disclose any classified information.

The report lays blame at Canada's Foreign Affairs Department for incorrectly classifying a diplomatic document and distributing it to too many people. It was distributed to more than 200 government officials.

Opposition New Democrat party leader Jack Layton said he's not surprised that Brodie and Wilson were cleared.

"This was a report prepared by employees of Mr. Harper, about employees of Mr. Harper that concluded that nothing could be found that could be pinned on the employees of Mr. Harper in any definitive or final sense," Layton said.

The report suggested the diplomatic row was prompted by comments Brodie made to a Canadian Television reporter on background during a budget briefing in Ottawa. Brodie reportedly downplayed talk by Clinton that the two countries would reopen the North American Free Trade Agreement, but Brodie said he didn't remember saying such a thing.

Brodie told investigators that while visiting the Canadian embassy in Washington the day before, he heard someone say something about a back-channel assurance from one of the campaigns. Brodie said he assumed the remark was about Clinton because there was a story in the news on Clinton's remarks about renegotiating NAFTA.

Some U.S. Democrats, as well as Canadian opposition parties, accused Harper's Conservative government of meddling in the U.S. primary elections. Canadian opposition parties demanded Brodie be fired.

The Clinton campaign "flatly denied" the suggestion that a Clinton adviser had told Canadian government officials to take the candidate's tough talk on NAFTA with "a grain of salt."

Some blamed the furor for Obama's loss in the Ohio primary in March. The story that the Obama campaign may have downplayed his stance on NAFTA received more attention than the story that Clinton may have done the same thing.

Both Obama and Clinton said earlier this year they would use the threat of pulling out of NAFTA to persuade Canada and Mexico to negotiate more protections for workers and the environment in the agreement. NAFTA is unpopular among working-class voters who say it has cost American jobs.

In a brief written statement Friday, Harper highlighted the findings of the report and said he has "accepted all the recommendations of the report."