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WASHINGTON (Reuters) - The White House is “very optimistic” it will reach a so-called phase one trade pact with China before the end of the year, a senior administration official said on Friday, adding that a deal would likely be struck before more tariffs take effect in mid-December.

“We’re very optimistic that round one will be completed and, hopefully, signed before the end of this year,” Marc Short, chief of staff to Vice President Mike Pence, told CNBC.

Asked whether a deal would be reached before the United States puts more tariffs on Chinese imports on Dec. 15, Short said: “I think that it’s likely within that time line, but I don’t want to try to tie Mnuchin and Lighthizer’s hands to a specific deadline, because I don’t think there is one.”

Short was referring to U.S. Treasury Secretary Steve Mnuchin and U.S. Trade Representative Robert Lighthizer, the top two American negotiators in talks with China.

Officials from both countries on Thursday said China and the United States had agreed to roll back tariffs already put in place on each others’ goods in a “phase one” deal, but the idea has been met with stiff opposition within some quarters of the Trump administration.

Trump, in comments that hit stock prices and the dollar, said on Friday he had not agreed to a tariff rollback.

“I haven’t agreed to anything,” he told reporters at the White House.