WASHINGTON — President Trump said on Monday that the United States would soon announce a “reciprocal tax” on countries that take advantage of the United States on trade, including trading partners he described as “so-called allies.”

“They’ll send in their product, and we won’t charge them anything,” the president said during a meeting with mayors and governors to discuss his proposal for rebuilding American infrastructure. “And we send them our product — same product as they’re sending us — and they’ll charge us 50 and 75 percent tax, and that’s very unfair.”

Though the president said more information would be forthcoming as soon as this week, White House officials quickly played down his comments, with one senior administration official saying that the proposal was “nothing formal right now.”

“The reciprocal tax is, simply, what you do to us, we’ll do to you,” the official said.

But when it comes to imposing reciprocal tariffs, trade analysts said the president’s hands were somewhat tied. The relatively low tariffs that the United States charges on many foreign goods were hammered out through decades of bargaining and bartering at the World Trade Organization.