WASHINGTON (Reuters) - The United States wants Vietnam to release some "prisoners of conscience" in the coming weeks as the U.S. Congress weighs its approach to a Pacific Rim trade treaty, a senior U.S. rights official said on Friday.

The Trans-Pacific Partnership (TPP), a 12-nation trade pact that would stretch from Japan to Chile, could be a boon to the Vietnamese economy and is a key point of U.S. leverage as it seeks to push Vietnam to improve its human rights record.

"In the short term, we would like to see, of course, prisoners of conscience released," U.S. Assistant Secretary of State for Democracy, Human Rights and Labor Tom Malinowski told a small group of reporters.

"We want to see things moving in the right direction in Vietnam, not in the wrong direction," he added, saying that the Vietnamese authorities now held just over 100 such prisoners, down from just over 160 in 2013.

The TPP cleared a crucial test on Thursday when the U.S. Senate voted 65-33 to proceed with consideration of so-called "fast-track" trade legislation, under which Congress can approve or reject trade deals but cannot amend their details. The U.S. House of Representatives has yet to take up the issue.

"I left the Vietnamese government with the very clear message that what they do on these issues, particularly in the next few weeks, will have a very significant impact on the prospects for TPP and other things that they want," Malinowski, who returned from a trip to Vietnam this week, said.

(Reporting by Arshad Mohammed; Editing by Will Dunham and Susan Heavey)