Lashing out at the longtime US ally and northern neighbour, President Donald Trump tweeted that Canadian Prime Minister Justin Trudeau is "dishonest & weak" and that the US was pulling back its endorsement of the G7 summit's communique in part because of what he called Trudeau's "false statements" at a news conference.

In an extraordinary set of tweets aboard Air Force One, on its way to Singapore for Tuesday's summit with North Korea's Kim Jong Un, Trump threw the G7 summit into disarray Saturday and threatened to escalate his trade war just as Canada released the G7's official communique.

AAP