Bangkok - The number of political prisoners in Myanmar jails has almost doubled to more than 2,000 over the past year, a report compiled by anti-government activists revealed on Sunday.

Myanmar's prisons now hold 2,123 political prisoners, compared with 1,192 in June 2007, the last time the United Nations ventured an estimate on inmates in the military-run state, according to a report compiled by the Thailand-based Assistance Association for Political Prisoners (Burma) and the US-based US Campaign for Burma.

"Dramatic increases in the number of political prisoners show the junta's defiance of the United Nations and international community, as well as its own people," said the two pro-democracy activist groups in a joint letter to UN Secretary-General Ban Ki-moon and other members of the UN Security Council.

The UN has been calling on Myanmar's ruling junta to release all its political prisoners, including opposition leader and democracy icon Aung San Suu Kyi, for decades to little avail.

However, last month, the regime released Win Tin, 79, the country's longest-serving political prisoner as part of a broad amnesty in which more than 9,000 prisoners of various categories were freed.

Win Tin, 79, was a prominent journalist before he was arrested in 1989. He has spent 19 years in prison.

But only ten of the 9,000 freed inmates were political prisoners and one, Win Htein, was re-arrested the day after his release.

Suu Kyi, the leader of the opposition National League for Democracy Party, has been under house arrest for almost 13 of the past 19 years.

"We especially request Secretary General Ban Ki-moon to secure the release of all political prisoners in our country before, or during your visit to Burma in December," said the letter addressed to the US Security Council from the two activist groups. (dpa)