"It's sitting on Nancy Pelosi's desk," Trump told reporters in Oval Office.

"She's incapable of moving it. It looks like she can't. Everybody knows it's a great deal. She knows its a great deal," he said.

The leaders of the U.S., Mexico, and Canada signed the accord last year, but the deal requires the legislature in each country ratify the pact before it takes effect.

Democratic lawmakers in the U.S. House of Representatives have signaled support for the measure, but Speaker Pelosi - backed by some major American labor unions - has said she wants to see better enforcement mechanisms to strengthen workers' rights.

Mexico's president on Monday said he would send a letter to Pelosi pressing her to get the agreement through Congress.

The delay has outraged the Republican president, who sees replacing the existing North American Free Trade Agreement as fulfillment of a 2016 campaign promise.

"A lot of time is being wasted," Trump complained, blaming Pelosi.

"You're going to have Mexico and Canada pull it. Pretty soon. And if they do it's her fault. Not mine. We gave you a great deal. It's her fault."