REUTERS: Former US President Barack Obama on Wednesday voiced his support for Canadian Prime Minister Justin Trudeau, who faces a tough battle for re-election next week.
"I was proud to work with Justin Trudeau as President," Obama said in a tweet. "He's a hard-working, effective leader who takes on big issues like climate change. The world needs his progressive leadership now, and I hope our neighbours to the north support him for another term."
The two progressive leaders formed a close friendship which continues to be a popular topic on social media several years after Obama left the White House. They were spotted having dinner together at an Ottawa restaurant earlier this year.
Trudeau was the first Canadian prime minister the United States honoured with a state dinner in almost two decades, when Obama invited him and his wife to Washington in March 2016 after the prime minister won power the previous October.
The Canadian leader faces a much tougher fight this time, and polls strongly suggest he will lose his majority in parliament after the Oct 21 election.
This is not the first time Obama has endorsed a foreign leader. He tweeted his support for Emmanuel Macron ahead of France's 2017 presidential election.
The American embassy in Ottawa declined to comment on the endorsement on the grounds that Obama is a private citizen.
The Liberals, the Conservatives and the New Democrats - the three main parties contesting the vote - did not immediately respond to requests for comment.
Elections Canada, the country's nonpartisan elections administrator, said Obama's tweet did not contravene regulations on foreign interference.
"It's free speech. The only issue would be if Mr. Obama started to spend money on Mr. Trudeau's campaign," spokesman Pierre Cadieux said by phone.