Vietnam and American business leaders were disappointed on Tuesday after the US House of Representatives failed to pass a bill establishing permanent normal trade relations between the former enemies.
The surprise result raises the possibility that President George W. Bush could go to this weekend's Asia Pacific Economic Co-operation (Apec) summit in Hanoi without delivering on a trade initiative his administration had made a major priority.
Vietnam Foreign Ministry spokesman Le Dung told Reuters the vote was "very regretful, and not suitable, and not serving the mutual interest and wishes of the peoples of the two countries".
"It is especially not suitable with the wishes of American businesses," he said.
Congress needs to approve permanent normal trade relations with Vietnam for US farmers, bankers and other businesses to share in the market-opening benefits of Hanoi's entry into the World Trade Organisation next month.
The vote threatened to overshadow other efforts to ensure Bush's visit would be a success, including Vietnam's removal on Monday from the US list of countries that violate religious freedom. The State Department cited an improvement in Hanoi's tolerance for religious expression, but critics disagreed.
"Violations such as forced renunciation of faith and new arrests and detentions of religious leaders continue in Vietnam," said Felice D. Gaer of the US Commission on International Religious Freedom.
Vietnam's state-supervised religious umbrella group welcomed the decision. "This decision reflects accurately the reality in Vietnam," said Ngo Yen Thi, Director of the Government Committee for Religious Affairs.
On the trade bill, supporters failed to get the two-thirds vote needed to approve it on the House "suspension calendar", usually reserved for non controversial legislation. It is still possible that both the House and the Senate could approve the bill before Bush is in Hanoi.