WHISTLER - Fraught high-level meetings between the world's top economies were due to draw to a close on Saturday as the United States faced a unified opposition to President Donald Trump's escalating, multi-front trade offensive.

Outraged leaders from the world's major economies launched legal challenges Friday after announcing countermeasures to retaliate against harsh steel and aluminum tariffs which Trump allowed to take effect.

Individual ministers from Group of Seven nations were expected to brief the press but no joint final statement was planned, a sign of the strong discord as the world's major economies verged on open trade conflict.

Trump's imposition of tariffs on America's largest foreign providers of the crucial metals -- the European Union and Canada are the largest US exporters of steel and aluminum respectively -- upended the agenda for this normally convivial event for consensus-building among countries which account for about half of global GDP.

Finance ministers at this snow-capped mountain resort north of Vancouver, British Columbia instead spoke of exasperation and an abiding sense of betrayal by a long-time ally.

"Everyone expressed their complete incomprehension of the American decisions and everyone said it was up to the Americans to take the next step since they were the ones who imposed the tariffs," French Finance Minister Bruno Le Maire told reporters after a day of meetings concluded on Friday.

- Getting an earful from allies -

Chairing the meeting, host nation Canada's Finance Minister Bill Morneau allowed participants to register grievances with US Treasury Secretary Steve Mnuchin one at a time, according to a Canadian source.

Behind closed doors, Mnuchin listened but spoke little, saying instead the discussion could continue at next week's G7 summit in Quebec, Canada at which Trump is expected to participate, according to several sources briefed on the talks.

But the week's whirlwind global developments in trade suggested de-escalation was unlikely. In Washington on Friday, Trump mooted the possibility of scrapping the 24-year-old North American Free Trade Agreement in favor of seeking bilateral agreements with Canada and Mexico.

G7 governments were also digesting Trump's threats to impose tariffs on hundreds of billions of dollars in US auto imports on purported national security grounds. In China, US Commerce Secretary Wilbur Ross was due to conduct trade talks with Chinese officials even as Washington finalizes planned sanctions on Beijing -- including restrictions on Chinese investment in the United States, new export controls and 25 percent tariffs on about $50 billion in Chinese tech-sector goods.

The talks come despite Washington's apparent announcement last month of a truce with Beijing following talks in Washington last month.

China has threatened to hit back with tit-for-tat tariffs on tens of billions of dollars in US goods -- as have EU, Canadian and Mexican authorities, who have targeted goods manufactured in key US political districts that could weaken Trump's hand after November's mid-term elections.

The final list of Chinese imports affected by US tariffs will be announced June 15 and imposed shortly thereafter, while the proposed investment restrictions and enhanced export controls will be announced by June 30, according to the White House.

"China's door for negotiation remains open," said foreign ministry spokeswoman Hua Chunying on Friday.