Asked whether the two companies would be covered by the proposal, Yellen said: "It will include large profitable firms and those firms, I believe, will qualify by almost any definition."

The joint statement by G7 finance ministers earlier on Saturday said it would tackle tax avoidance by "the largest and most profitable multinational enterprises".

Amazon has lower profit margins than most other tech companies, and European countries had been concerned it would escape extra taxation under initial U.S. proposals to the G7.

(Reporting by Andy Bruce and David Milliken; editing by Michael Holden)