Thich Quang Do, the patriarch of the banned Unified Buddhist Church of Vietnam and a defiant champion of religious freedom, democracy and human rights in his country, died on Saturday. He was 91.

His death was confirmed by the Paris-based International Buddhist Information Bureau, an arm of his church. There was no information on where he died. A spokeswoman for the organization said that the Vietnamese authorities had held him incommunicado at the Tu Hieu Pagoda in Ho Chi Minh City and that it had been impossible for members of his organization to make contact with him. He had diabetes and a heart condition for many years, she added.

Thich Quang Do had for decades repeatedly challenged, and angered, the Communist government on issues of religious and political freedom and had effectively been under house arrest since 2003. He had spent the last 30 years or so in and out of prison, under house arrest or forced into internal exile for refusing to submit the Unified Church to government control.

He issued a stream of public statements over the years, putting him in the forefront of religious activism in Vietnam, which permits only a single government-sanctioned Buddhist organization. The Unified Church, founded as an umbrella organization for various Buddhist sects in 1964, was banned.