"The humanitarian sentiments shown by the authorities a year ago have now, regrettably, ended," she said, adding that she reiterated "the EUs call for the release of all peaceful advocates of human rights in Vietnam."

Ashton regretted "the failure by an otherwise much-valued partner country - with a fine record of poverty reduction and playing an increasingly responsible role in the world - to measure up to international standards of respect for basic, universal human rights, including freedom of expression.".

The United States and international rights groups have also urged authorities in Hanoi to free the priest, who was sentenced to eight years in prison in 2007 for propaganda against the state.

The sentence was suspended for a year in March last year when a series of strokes led to his partial paralysis and grave risk of death.

Prosecutors in Vietnam say Ly - who was taken into custody on Monday - was a founding member of the banned "Bloc 8406," considered by analysts as the first organised pro-democracy coalition inside the country.

Ly's arrest followed months of uncertainty over his sentence after the expiry of a one-year suspension of his prison term ordered by a court in March 2010.

Agence France Presse - July 30, 2011