Burmese exiles say security forces in military ruled Burma have arrested the prominent political activist Nilar Thein.

Two news agencies run by exiled Burmese journalists, Mizzima and the Democratic Voice of Burma, report Thursday that Nilar Thein was detained Wednesday evening in Rangoon's Yan Kin district. Nilar Thein is one of the leading members of the 88 Generation Students, a pro-democracy group that organized mass demonstrations 20 years ago to challenge the rule of Burma's military government.

The reports say she went into hiding a year ago after joining peaceful pro-democracy protests that were crushed by the military.  Her husband, Kyaw Min Yu, was arrested for joining the demonstrations.

U.N. Secretary-General Ban Ki-moon expressed frustration Thursday about the situation in Burma. He said the country has not made the political progress he had hoped for, including an inclusive political process with human rights.

A military government has ruled Burma since 1962, and has been widely criticized for suppressing basic freedoms.

The opposition National League for Democracy won general elections in 1990, but the country's military leaders refused to relinquish power.  It has kept pro-democracy leader and Nobel peace laureate Aung San Suu Kyi under house arrest for 13 of the past 19 years.