The US rights activist released yesterday from a Burmese prison has described how he was tortured during interrogation by intelligence agents last year.

Burmese-born Kyaw Zaw Lwin, also known as Nyi Nyi Aung, arrived in Bangkok airport yesterday after being held in detention since September last year.

He told DVB that he had been taken to Rangoon’s Insein prison from another prison on the evening of 17 March and informed by prison authorities that he was going to be released the next morning.

“I began to realise I was going to be released. As my [mother and cousins] are imprisoned I was met by my relatives in Insein prison’s guest room,” he said.

A diplomat at the US embassy in Rangoon officially announced his release yesterday. Kyaw Zaw Lwin was asked to sign an agreement “vowing that I acknowledge that I will have to serve my remaining prison sentence if I get charged again in Burma”.

The activist’s aunt, Khin Khin Swe, said that he was accompanied to the plane by the US embassy counsellor.

Kyaw Zaw Lwin went on to describe how he was “mentally and physically tortured” after being arrested at Rangoon airport on 3 September, following which he was convicted on charges of fraud and forgery and sentenced to three years with hard labour.

“I was punched and had my fingers bent and also threatened with a knee to the face. I wasn’t allowed to lie down for 12 days in a row [during interrogation] and then another 14 days before I was sent to the prison,” he said.

Critics of the ruling junta in Burma said that he was being punished for his high-profile activist work, which included delivering a petition with 600,000 signatures to UN chief Ban Ki-moon calling for the release of political prisoners in Burma.

“I was arrested without a warrant as some as I came out of the plane. I believe it was politically motivated; I was detained for a reason I don’t know,” he said. “I didn’t break any law – I am a person working to bring about a change for Burma and its people’s freedom.”

The reason for his early release remains unclear. His arrest and sentencing drew international condemnation, and the US has repeatedly called for his release, although there had been little inkling prior to Wednesday that this would take place.

Both his mother and two cousins remain in prison in Burma following their role in the September 2007 monk-led uprising. One cousin was given a 65-year sentence.

“In our country the administrative, the legal and the justice pillars have no independence,” he told DVB. “These are merely surviving under the rulers of the country.”