Myanmar Thursday released a US rights activist jailed for fraud and forgery in a rare show of leniency ahead of elections this year.

Democracy advocate Kyaw Zaw Lwin was "thrilled" to be going home, his fiancee said, after he was given a three-year term in February for forging an identity card, failing to declare currency at customs and violating immigration law.

Supporters of the Myanmar-born US citizen, also known as Nyi Nyi Aung, said he had travelled to the country to visit his ailing mother, herself detained for political activities, when he was arrested on September 3.

The 40-year-old had been behind bars in Yangon's notorious Insein prison since, despite an appeal by more than 50 US lawmakers who wrote to Myan-mar's leader, Senior General Than Shwe, for his release.

"I spoke with him and he was very strong, in high spirits and so thrilled to be free," his fiancee Wa Wa Kyaw, a nurse in the Washington area, told AFP.

But she said Kyaw Zaw Lwin, who was spending the night in Bangkok as he awaited a flight to the US, felt pain in one of his legs after his detention.

Drake Weisert, a spokesman for the US embassy in Yangon, confirmed in an email to AFP that Kyaw Zaw Lwin had left Myanmar.

Officials from the southeast Asian nation, asking not to be named, earlier said authorities were deporting the US man Thursday afternoon but gave no legal explanation.

His lawyer Nyan Win, who also represents detained opposition leader Aung San Suu Kyi, was initially unaware of his release after an appeal against the sentence was rejected, but later said he was glad of the news.

The US has changed diplomatic tack in recent months, seeking greater engagement with the Myanmar government after years of isolation, while maintaining sanctions.

But US officials have remained vocal in their criticism, only last week slamming plans for this year's polls as "devoid of credibility" as they prevent opposition leader Suu Kyi and other political detainees from taking part.

The United States had said Kyaw Zaw Lwin's conviction was "unjustified" and called for his release.

Despite this, the prisoner's fiancee had said she felt betrayed by the US government and sought further efforts to secure his freedom.

AFP