The United States has welcomed the release of an environmental activist in Turkmenistan who had been sentenced to three years' imprisonment last month for illegally leaving the central Asian country and concealing a plot against its authoritarian president, Saparmurat Niyazov.

The United States has been a persistent critic of the Niyazov government's human rights record. But it is welcoming the release of environmentalist Farid Tukhbattullin, whose closed trial, and sentencing March fourth had drawn international condemnation.

Mr. Tukhbattullin, an activist in Turkmenistan's small environmental movement, was given a three-year prison term for illegally crossing the Turkmenistan-Uzbekistan border last November to attend a conference in Moscow, and of concealing an assassination plot against the president.

His arrest was part of a wide-ranging crackdown on dissent in the country which followed a gun attack on President Nizayov's motorcade November 25 which the government depicted as an attempted coup led by Niyazov critics including former government officials.

According to reports in the country's government-controlled media, the 42-year-old Mr. Tukhbattullin was granted a presidential amnesty after admitting his guilt and expressing deep repentance. What was said to be a confession was carried by Turkmen newspapers Wednesday.

In a written statement here, State Department spokesman Philip Reeker said that since Mr. Tukhbattulin's trial was neither transparent nor in accord with international standards of due process, the legitimacy of the confession "is open to question."

Nonetheless, Mr. Reeker said Mr. Tukhbattulin's amnesty is "a welcome step." He said the United States urges the Turkmenistan government to respond in a similar, positive, fashion to other human rights appeals by the United Nations and the Organization for Security and Cooperation in Europe (OSCE).

The OSCE representative in Turkmenistan also welcomed the release and suggested it might be linked to scrutiny of the country's rights record at the on-going meeting of the U.N. Human Rights Commission in Geneva.

In its annual worldwide report on human rights issued Monday, the State Department described Turkmenistan's human rights record as "extremely poor" and said the situation in the country "deteriorated markedly" after the November attack on the president.

The report said Mr. Niyazov, a Soviet-era Communist Party chief and the country's only leader since independence in 1992, held a "monopoly on political power" aided by a powerful national security ministry and police force which both committed human rights abuses.