The White House added more pressure on China to revalue its yuan currency on Friday, saying the world would be better off if Beijing implemented a market-based exchange rate.

This is obviously going to be an issue that we'll continue to discuss, White House spokesman Bill Burton told reporters on board Obama's aircraft as it flew to Ohio.

His comments came after the White House released a letter from Obama to G20 leaders that said free-floating currencies were essential to global economic activity.

(Reporting by Matt Spetalnick, writing by Jeff Mason, editing by Stacey Joyce)