A prominent Buddhist monk who was one of the leaders of a 2007 anti-government uprising has been detained for questioning by Myanmar authorities, less than a month after he was freed from jail.

Gambira was one of hundreds of political prisoners released in January, cutting short a 68-year jail term imposed for his key role in the 2007 "Saffron Revolution", which was brutally crushed by the former junta.

Since he was freed, Gambira has breached regulations by breaking into monasteries closed by the government after the mass monk-led demonstrations, a government official told AFP Friday on condition of anonymity.

"He was taken this morning from his monastery for questioning because he broke the locks of three monasteries since his release," the official said, adding that he was taken in Yangon in the early hours of the morning.

The government's release of about 500 political prisoners since October has been hailed by Western countries, which have long demanded the freeing of such detainees before they would consider lifting sanctions.

A quasi-civilian regime, which came to power in March last year after almost half a century of outright military rule, has impressed observers with its apparent desire to reform and open up to the outside world.

A key sign of change has been the rehabilitation of the junta's public enemy number one Aung San Suu Kyi, who was released from house arrest soon after a 2010 election and has since been allowed to launch a bid to enter parliament.

The democracy campaigner is running in April 1 by-elections after her National League for Democracy (NLD) party was welcomed back into the political mainstream.

Observers and the international community are set to closely watch the upcoming vote, mindful of the widespread criticism and accusations of cheating in 2010, and have called on the government to ensure it is free and fair.

The 2007 protests that landed Gambira in jail began as small rallies against the rising cost of living but escalated into huge anti-government demonstrations led by crowds of monks.

They posed the biggest challenge to military rule in nearly two decades, leading to a bloody crackdown by the authorities. At least 31 people were killed by security forces while hundreds were beaten and detained.

Other key figures freed in January include Min Ko Naing, one of the most prominent opponents of the regime.

The 49-year-old activist played a leading role in a 1988 student uprising that was crushed by the army. He was detained in 1989 and spent 16 years in jail.

His latest stint in jail stemmed from his third arrest in 2007 for his role in that year's demonstrations. He was sentenced to 65 years.