Washington — President Donald Trump opened his meeting on Friday with newly elected South Korean President Moon Jae-in with tough trade talk, announcing he is renegotiating a 5-year-old trade deal between their two countries that was a joint legacy of President George W. Bush and President Barack Obama.

Yet it was unclear from his and administration aides’ remarks how significant a break Trump was making with a free-trade agreement that had broad support when it was approved by Congress. Trump’s announcement could be seen as a provocation of an ally at a delicate time, when the administration is looking to South Korea to help contain North Korea’s nuclear program.

“It’s been a rough deal for the United States, but I think that it will be much different and it will be good for both parties,” Trump said in a joint appearance with Moon in the Oval Office. “We want something that’s going to be good for the American worker.”

Moon said nothing publicly to confirm that a full-scale renegotiation had begun. He said the agreement benefits both countries, and they can address specific concerns if necessary. Trump’s public criticism of South Korea’s trade surplus with the United States could cause Moon embarrassment at home, and increase pressure against U.S. demands for a harder line against North Korea.

Congressional approval would likely be required for major changes. White House spokeswoman Sarah Huckabee Sanders said the U.S. trade representative, Robert E. Lighthizer, is calling a joint committee meeting with his Korean counterparts that would start the process of amending the deal.

She dismissed questions about the impact on the U.S. security relationship with South Korea. Its embassy didn’t respond to a request for comment.

“It sounds like the president got ahead of himself,” said Wendy Cutler, a former trade official who was the lead negotiator on the deal for Bush and Obama.

Cutler, vice president of the Asia Society Policy Institute, said Trump does not appear to have support from South Korea and would need close consultation with Congress.

“It seems to me this was kind of a one-sided announcement,” Cutler said in a phone interview from Tokyo before a scheduled visit to South Korea on Monday.

Trump has complained about the trade deficit with South Korea, which was $17 billion for goods and services in 2016, according to the U.S. trade office. In April, he told the Washington Post that he would consider ending or amending the trade agreement with Seoul.

But the trade relationship is an important one. South Korea is America’s sixth-largest goods trading partner, with $112.2 billion exchanged between the two countries last year.

The U.S.-Korea Free Trade Agreement was negotiated and signed by Bush in 2007, and then renegotiated and implemented under Obama in 2012.

Commerce Secretary Wilbur Ross said the trade imbalance between the countries has doubled since the agreement, and he blamed South Korea for restricting imports of U.S. cars through strict regulations.