U.S. trading partners have been furious over President Donald Trump's decision last week to impose tariffs on steel and aluminum imports from Canada, the European Union and Mexico as part of his "America First" agenda.
Earlier, Mr Trudeau had spoken of retaliatory measures that Canada would take next month in response to Mr Trump's decision to slap tariffs on steel and aluminum imports from Canada, Mexico and the European Union.
Donald Tusk, president of the European Council, said that Trump's determination to bait his allies over trade and diplomatic engagements "would only play into the hands of those who seek a new post-West order where liberal democracy and fundamental freedoms would cease to exist". "The countries have to remain polite as the USA is an ally and we need them".
The president's Twitter outburst, sent as he flew to an historic meeting with North Korea's ruler Kim Jong Un in Singapore, unravelled days of work by the world's top nations in attempting to resolve a global trade dispute.
He said: "Why are we having a meeting without Russian Federation in the meeting?"
Despite the president describing his relationship with the other leaders as "a 10", conversations between the world's largest industrialized countries were thought to be intense as the allies faced off with Trump over tariffs his administration has imposed on them.
The U.S. and the rest of the G-7 countries - Britain, Canada, France, Germany, Italy and Japan - depend on each other for security and as economic partners, so the governments will have incentives to find some common ground.
The two leaders talked on the phone last week after Trump announced US tariffs on European goods.
US President Donald Trump is seated amid a crowd of officials.
Some media, though, interpreted the photo as another embarrassing moment for the U.S. Esquire sighed that the photo proved how Trump was still alienating our allies.
Mr Trump will skip G7 meetings about climate change, clean energy and ocean protection.
Later, the United States president tweeted: "Prime Minister Trudeau is being so indignant, bringing up the relationship that the USA and Canada had over the many years and all sorts of other things...but he doesn't bring up the fact that they charge us up to 300% on dairy - hurting our Farmers, killing our Agriculture!"
Instead, Canada's expected to issue a chair's summary of the meeting. "I'd even wish for that to happen - that two presidents meet for an extended period of time".
Asked if she was concerned that Trump could retaliate against European Union counter-measures by imposing tariffs on cars, Merkel said: "First of all, we'll try and see if we can prevent this". But it won't solve the differences, particularly on trade, with the European Union moving toward retaliatory tariffs from July on key US goods.
A German official said that if Trump declines to sign a communique, it won't be the end of the G-7, but it would be a worrisome signal.
Trump aide says ‘there’s a special place in hell’ for Justin Trudeau
In an interview Sunday on German public television, Merkel also says European leaders won't be "taken advantage of" on trade. Trump's trade adviser Peter Navarro also lashed out on Sunday at Trudeau's statements , saying they represent "bad faith".