Vietnamese worshippers face raids, confiscations and arrest if they practice their faith outside of government-sanctioned institutions, constituting what U.S. officials say is a major obstacle to improved bilateral relations.
Certainly, there are opportunities to worship in Vietnam, where religious freedom is guaranteed by the constitution. Whether one is a Christian, Buddhist or Muslim, there are plenty of places to attend services and meet fellow believers without fear of raids or arrests.
But that freedom extends only to officially approved organizations, which are subject to broad government control over their activities. Any religious group unwilling to submit to that control can only organize illegally, in which case the government assumes the right to persecute its members and confiscate its property.
Vietnam's communist rulers "want to control everything," said the Rev. Nguyen Hong Quang, one of the leaders of the banned Vietnam Mennonite Church. "They want all religions to serve them. They require that all pastors support their policies, so they can use the churches as propaganda machines."
Mr. Nguyen, 45, said in an interview that he has been arrested more than 40 times and jailed on five occasions.
He was "attacked" by undercover policemen Dec. 9, he said, as he was leaving a friend's house in Ho Chi Minh City, formerly Saigon. He was not detained, but the police arrested the Rev. Pham Ngoc Thach, a fellow Mennonite minister who was giving Mr. Nguyen a ride on his motorcycle. They accused him of possessing illegal proselytizing materials.
Mr. Ngoc, who accompanied Mr. Nguyen during the interview, said he was detained for about 24 hours at the Nguyen Thai Binh police station in the city's center, where he was tortured with electric shock. His accusation could not be confirmed.
Both Vietnamese and foreigners agree that the level of religious tolerance in the country has improved significantly since the end of the Vietnam War in 1975.
The latest State Department report on religious freedom also made that point, but said that "strict restrictions on the hierarchies and clergy of religious groups remained in place, and the government maintained supervisory control of the recognized religions.
"The Communist Party fears that not only organized religion, but any organized group outside its control or supervision may weaken its authority and influence by serving as political, social and spiritual alternatives to the authority of the central government."
One U.S. official engaged in U.S.-Vietnamese relations said that "everything that goes well between the United States and Vietnam is contaminated by" the issue of religious persecution.
He said Vietnamese are told at every meeting between the two countries: "We have such a wide-ranging relationship now, we developed it so quickly and so completely, and yet the more you persist in violating the individual rights of these people, the more you poison the entire relationship."
Vietnamese authorities, however, are not very receptive to criticism from their former wartime foes, which they dismiss as interference in their internal affairs.
"The United States bombed Vietnam and, in the minds of many people, it is unacceptable for it to criticize human rights," said Le Linh Lan, director of the Center for European and American Studies at the Institute of International Relations in Hanoi.
"The U.S. comes to the table with a list of demands and we are supposed to live up to them, and that is not acceptable," she said. "Open and frank discussion would be OK, so we can better understand each other."
In the meantime, police raids and arrests remain common at the thousands of underground "house-churches" throughout the country, Mr. Nguyen said. He estimated that more than 3,500 religious groups in Vietnam are being targeted by authorities.
The Mennonites, a Christian group with about 11,000 members and 130 house-churches, "believe in peace and oppose war and demonstrations," Mr. Nguyen said.
"We are also against others, especially the government, getting involved in our affairs," he said. More than 200 Mennonites in Vietnam are in jail for their beliefs, according to the group.
But Vietnamese officials, who say the banned religious groups are actually disguised political organizations aimed at overthrowing the government, have turned the issue into a matter of national security.
Ngo Yen Thi, chairman of the Government Committee for Religious Affairs, said the authorities have a responsibility to protect the social order.
"The state respects and ensures the right of religious freedom, and all religious groups are equal before the law, as long as their activities don't affect the order of society," he said in an interview in his Hanoi office.
"We also have to consider if a religion is righteous," he added.
Mr. Ngo accused some groups of engaging in "spontaneous religious activities that are harmful to the health of the people," such as drinking and sex orgies.
"People gather wearing nothing and having sex in one room and they call it religion," he said.
About a third of Vietnam's population is not religious. Nearly half are Buddhist and about 10 percent are Catholic. The other major religions are Cao Dai, Hoa Hao, Protestantism and Islam.