The Trump administration showed no sign of backing down from restrictive tariffs in the face of pushback from allies and China over the weekend, isolating the U.S. and complicating the president’s meeting later this week with leaders of Washington’s staunchest partners.

Top finance officials from the Group of Seven leading nations last week met in Canada, where the non-U.S. members issued a public rebuke of Washington’s new steel and aluminum tariffs. Those six—the host Canada, along with France, Germany, Italy, Japan and the U.K.—adopted a formal statement Saturday expressing their “unanimous concern and disappointment.”

The following day in China, Beijing said it wouldn’t abide by any agreement to buy more U.S. products without assurances that the U.S. wouldn’t go ahead with plans to hit it with tariffs on $50 billion Chinese imports.

But even with retaliatory moves under way in China as well as in Europe and North America, there was no sign over the weekend that the administration was wary of inching closer to a trade war.

“When you’re almost 800 Billion Dollars a year down on Trade, you can’t lose a Trade War!” President Donald Trump said in a Twitter message Saturday. “The U.S. has been ripped off by other countries for years on Trade, time to get smart!”

The disputes come just as the Trump administration has its arms full of difficult negotiating tasks. Most immediately, Mr. Trump himself then must face leaders of countries who have termed his policies extreme, unwise and in some cases illegal when he arrives in Quebec for a summit of G7 heads of state scheduled for Friday and Saturday.

That will be followed by a planned summit with North Korea in Singapore just three days later, on June 12. Mr. Trump also is facing European opposition to his push to rewrite the 2015 Iran nuclear deal, and is planning for a summit with Russian President Vladimir Putin.

Treasury Secretary Steven Mnuchin, who attended the G7 finance officials’ meeting, denied the U.S. was left outside the consensus on all matters and insisted Washington is playing a central role. “I don’t think in any way the U.S. is abandoning its leadership in the global economy,” Mr. Mnuchin said.