FILE PHOTO: U.S. Trade Representative Robert Lighthizer takes part in a joint news conference on the closing of the seventh round of NAFTA talks in Mexico City, Mexico March 5, 2018. REUTERS/Edgard Garrido

WASHINGTON (Reuters) - U.S. President Donald Trump has appointed U.S. Trade Representative Robert Lighthizer to oversee a new round of trade talks with China aimed at defusing longstanding trade tensions and heading off a wider trade war, a White House official said on Monday.

Trump and Chinese President Xi Jinping agreed to hold off on new tariffs during talks in Argentina on Saturday, launching talks to resolve issues of concern against a 90-day clock.