SINGAPORE—A tariff agreement with Vietnam emphasizes one of the White House’s top priorities in this frantic round of dealmaking over global trade: Slamming shut any back door routes for Chinese goods to enter the U.

Vietnam on Thursday hailed as a breakthrough a long-awaited trade deal with the United States and said its negotiators were coordinating with U.S. counterparts to formalise terms with Washington,

Vietnam finds itself caught between its two biggest trading partners as the Trump administration tries to stop Chinese exporters using Vietnam as a way station.