OTTAWA -- Federal party leaders jousted over foreign policy, climate change and Indigenous issues during Thursday's English-language debate -- their last, best chance to sway voters before the Sept. 20 election.

Questions about the fall of Afghanistan and the ongoing imprisonment of Canadians Michael Kovrig and Michael Spavor in China ignited heated discussions between the five leaders invited to participate.

Conservative Leader Erin O'Toole, NDP Leader Jagmeet Singh, Green Party Leader Annamie Paul and Bloc Quebecois Leader Yves-Francois Blanchet piled on Liberal Leader Justin Trudeau for calling an election while Afghanistan was falling to the Taliban.

Trudeau shot back at his opponents, accusing them of talking down the work by the military and diplomats to get 3,700 people out of Afghanistan, and 43 more with the help of Qatar earlier Thursday.

Trudeau also said his government is doing everything it can to get Kovrig and Spavor, known in Canada and around the world as the "two Michaels," out of China.

"If you want to get the Michaels home, you do not simply lob tomatoes across the Pacific," he told O'Toole.

The federal leaders also sparred over Indigenous reconciliation, with Paul saying the issue should not be treated like a buffet.

Singh accused Trudeau of "taking a knee" -- as he did at an anti-racism rally on Parliament Hill last year -- while taking Indigenous kids to court.

Singh was referring to Ottawa's controversial legal challenge of a pair of rulings involving First Nations children.

Trudeau shot back, saying cynicism is harming reconciliation efforts, and that his government has made progress by getting more Indigenous kids into quality schools and lifting more than 100 boil-water advisories.

O'Toole said he would like to see the Canadian flag raised again on Sept. 30, the National Day for Truth and Reconciliation, with a commitment to "move forward" on the calls to action from the Truth and Reconciliation Commission.

The Canadian flag has remained at half-mast on the Peace Tower and other federal buildings since late spring to mark the finding of unmarked graves on the grounds of former residential schools. O'Toole has previously said Canadians "should be proud to put our flag back up."

On climate change, Singh and Trudeau had a fiery exchange, with the Liberal leader saying the NDP's policy rates an 'F' while stating that experts have given the Liberal plan high marks.

Singh accused Trudeau of presiding over the worst record on fighting climate change in the G7 during his six years in power.

Paul said Canada could become a renewable energy superpower, and all parties need to work together to respond to the shared threat.

The two-hour debate began with tough questions from moderator Shachi Kurl, president of the Angus Reid Institute.

To Trudeau, it was why he called an election just as a fourth wave of COVID-19 was sweeping the country.

He argued that the debate would show voters have to choose among radically different views on how to finish the fight against COVID-19 and build back better.

To O'Toole, the question was how can voters trust that he would be in the driver's seat if elected prime minister, and not his caucus, many members of which have decidedly more conservative views on issues like abortion and climate change.

"I am driving the bus," O'Toole insisted, stressing that he's personally "pro-choice."

Singh was asked to explain why he has yet to release the costing for his election platform. He did not directly respond while saying the NDP is the only party that would make the ultrarich pay their fair share.

Blanchet took issue with Kurl asking him why he supports "discriminatory laws" in Quebec, which prohibit some public sector workers in positions of authority from wearing religious symbols.

He insisted the laws are not discriminatory but are legitimate laws that reflect the values of the Quebec nation.

Perhaps the most devastating question went to Paul, who was asked how she could hope to lead the country when she's been unable to lead her own party members, some of whom spent weeks prior to the campaign trying to dump Paul as leader.

Paul conceded she's been through a difficult period but said she's had to "crawl over a lot of broken glass" to get on the leaders' debate platform and is proud to be the first Black woman to do so.

People's Party of Canada Leader Maxime Bernier did not meet the independent Leaders' Debates Commission's criteria for participating in either the English-language debate or the French-language debate on Wednesday.

But dozens of his supporters showed up Thursday outside the debate venue -- the Canadian Museum of History in Gatineau, Que., just across the river from Parliament Hill -- to protest his absence.

The debate was the last of three to be held during the campaign and came 11 days before election day and just as four days of advance polls are set to open Friday.

Shortly before arriving for the debate, the five leaders got together to shoot a video urging all Canadians to get vaccinated against COVID-19.

"It was really important to let folks know that getting vaccinated is not a partisan thing," said Singh, who initiated the united message, as he made his way into the debate venue.

"I want you to vote for me but it doesn't matter who you vote for, all leaders agree getting vaccinated is one of the most important things we can do to fight this pandemic, to keep people safe."

This report by The Canadian Press was first published Sept. 9, 2021.