Prime Minister Justin Trudeau says the renegotiation of the North American free-trade agreement is "too important" for partisanship, after federal Conservatives went on a cross-border campaign to criticize the Liberal government for paying $10.5-million to former Guantanamo detainee Omar Khadr.

But Conservative Leader Andrew Scheer vowed Thursday to keep up his party's condemnation of the settlement, saying any negative outcome resulting from the Khadr payout lies with the government.

Senior Liberals this week suggested that the Tories' campaign against the government's settlement with Mr. Khadr could affect trade talks with the Trump administration, set to begin on Aug. 16 in Washington.

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Related: Liberals say Conservatives' Khadr campaign could impact NAFTA talks

Mr. Trudeau addressed the controversy on Thursday, saying Canadians have been pleased that various levels of government and different political parties are working together on the Canada-U.S. file.

"This is too important to fall into partisanship," Mr. Trudeau told reporters during a news conference in Barrie, Ont.

"Canadians expect their representatives, whatever party they be part of, to be standing up for Canadian interests and making sure that we are creating the right deal for Canada as we move forward on modernizing NAFTA."

Mr. Scheer, however, said he rejects the link the Liberals are making between the payment to Mr. Khadr and free-trade negotiations.

"The only people now who are trying to make this assertion are the Liberals themselves. And this comes on the heels of them desperately trying to deflect blame to others," Mr. Scheer said at a news conference in Ottawa, where he was introducing five members of his senior team, including new deputy leader Lisa Raitt.

"If they were so concerned about the backlash, I would ask, 'did they give anyone in the U.S. a head's up? Did they let their negotiating team in Washington know that it was coming? Did they talk to the State Department?'"

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The Trump administration has so far been quiet on the Khadr issue and a State Department official declined to comment when contacted on Thursday.

Still, Mr. Scheer said Conservatives will continue to present a "united front" in the United States on trade issues.

"I have instructed my members of Parliament … to speak with one voice as Canadians, to make sure that we're doing what's in the best interest of Canadian businesses and Canadian workers," Mr. Scheer said.

Mr. Khadr, a Canadian citizen, was sent to Guantanamo Bay at the age of 15 after he was accused of throwing a grenade that killed U.S. army medic Sergeant Christopher Speer and injured Sergeant Layne Morris in Afghanistan. The Supreme Court of Canada ruled in 2010 that the actions of Canadian officials who participated in U.S. interrogations of Mr. Khadr had offended "the most basic Canadian standards about the treatment of detained youth suspects."

Before the settlement, Mr. Khadr's lawyers had filed a $20-million lawsuit against the federal government.

Mr. Trudeau again defended his government's decision on Thursday, saying it would have cost much more to settle the case in court.

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"Obviously, people are troubled by the settlement, and as was I. And that's why we settled. If we had continued to fight this in court, we would have been spending three or four times as much money on a payout," he said.

"Previous governments systematically and deliberately neglected to defend and were even complicit in the violation of a Canadian citizen's rights. This is not about the facts of what Mr. Khadr did or didn't do. This is about what the Canadian government did or didn't do. And when a Canadian's rights are violated, everyone pays."

Mr. Scheer disputed Mr. Trudeau's argument about cost-saving, noting the Liberals settled out of court and have never publicly disclosed or explained the reported $10.5-million sum.

"Nobody believes that Justin Trudeau made this payment to save taxpayers' money," Mr. Scheer said. "We're running massive $30-billion deficits. The amount of money that he's claiming he would have saved would be a rounding error."

He added that the Conservatives accept the Supreme Court's ruling that Mr. Khadr's rights were violated, but said the matter of compensating Mr. Khadr "was worth fighting for" in court.

"Compensation was already provided to Omar Khadr. He was brought back to Canada, and able to enjoy the very rights and freedoms that he was fighting against in Afghanistan," Mr. Scheer said.

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On Sunday, the Wall Street Journal published an opinion piece from Conservative MP Peter Kent, called A Terrorist's Big Payday, Courtesy Of Trudeau, and Conservative MP Michelle Rempel appeared Monday on Fox News, the same day the U.S. administration released its sweeping list of more than 100 negotiating objectives for NAFTA. The Conservative Party also launched a website, "Khadr Questions," which invites visitors to tweet to Mr. Trudeau's government with questions and concerns about the payment. The site collects personal data from visitors, although a Conservative spokesman said it is not a fundraising initiative.

Mr. Khadr, now 30, spent more than 10 years in U.S. and Canadian custody, much of that time in Guantanamo. Once the youngest detainee there, he was transferred to Canada in 2012 after accepting a plea deal. He later recanted.