The coalition of 19 groups also wants Obama to tell Vietnam's authoritarian government that its repression of human rights endangers its participation in the 12-nation Trans-Pacific Partnership free trade pact, or TPP.

The groups made the appeal in a letter to Obama, who will visit Vietnam in May, becoming the third consecutive U.S. president to do so. Signatories of the letter include Freedom House, Human Rights Watch and Viet Tan.

On Monday, the U.S. and Vietnam concluded their annual human rights dialogue, where Washington pressed Hanoi over a recent spate of detentions of government critics and pushed for progress on legal reforms in the one-party state.

The rights groups said that as the U.S. Congress considers in coming months whether to ratify TPP, Vietnam must be made aware of the importance of acting now to confirm its commitment to the pact's human rights standards.

"Unfortunately, even in light of the agreements it has made as part of the TPP, Vietnam's crackdown on independent voices shows no signs of ceasing," the letter said.

It singled out the cases of imprisoned labor activists Doan Huy Chuong and Nguyen Hoang Quoc Hung; a Roman Catholic priest jailed for advocating for democratic reform, Father Nguyen Van Ly; and human rights lawyer, Nguyen Van Dai, who was arrested in December.

The letter concluded that Obama should make clear the U.S.-Vietnam relationship will not fundamentally advance without release of imprisoned activists, an end to the harassment of civil society groups, and respect for international law.

The Associated Press - April 26, 2016