"We're close. We're not quite finished yet, we're within range," Pelosi told a forum of chief executives on Monday evening.

Her office did not elaborate on any announcement but she will be accompanied at the news conference by Representative Richard Neal, the chairman of the Ways and Means Committee in the Democratic-led House of Representatives.

Pelosi told the forum she expected the final language of the USMCA to be set by Tuesday, which would bring Democrats to a "moment of truth" on whether to proceed to passage.

She was working on the language of separate legislation on how the deal would be implemented, she said.

The Trump administration and Democrats in the U.S. House of Representatives are closing in on a deal following several intense days of negotiations with Mexico over potential changes to clauses concerning labour enforcement, steel and aluminium, biologic drugs and internet services.

U.S. Trade Representative Robert Lighthizer and White House senior adviser Jared Kushner are due to fly to Mexico City on Tuesday for meetings to try to pin down final details, an administration official told Reuters on Monday.

They will be joined by Canadian Deputy Prime Minister Chrystia Freeland, a spokesman for Freeland said.

As House speaker, Pelosi will decide whether and when to bring the trade legislation to the floor for a vote.

(Reporting by Doina Chiacu; Editing by Angus MacSwan)