"The Turkmen regime is one of the most repressive in the world and it is high time that the international community take action," said Larissa Chikhmuradova, the sister of a Turkmen opposition figure who was arrested in December 2002 and sentenced to 25 years in prison.
"It remains very difficult for us to have reliable figures on prisoners of conscience," Sergei Nikitin, the head of Amnesty's Russia branch, told French news agency AFP.
In April, a UN human rights panel criticised the isolated former Soviet Central Asian republic for "repression of all opposition political activity," and urged the immediate and unconditional release of prisoners of conscience.
A resolution by the 53-member United Nations Human Rights Commission singled out restrictions imposed by President Saparmurat Niyazov's government on "freedom of thought, conscience and religion," arbitrary detention of those trying to exercise such rights, and discrimination against Russian and Uzbek minorities.
Niyazov has ruled the largely desert but gas-rich country on the eastern shore of the Caspian Sea and its five million people with an iron grip for almost two decades.