YANGON -- Myanmar's opposition said on Thursday the ruling military tried in vain to stop a crowd of 20,000 people flocking to a rally by Aung San Suu Kyi, reflecting growing political tension in the impoverished nation.

U Lwin, Secretary of Suu Kyi's National League for Democracy (NLD), told Reuters Suu Kyi had arranged to open an NLD Party office and make a speech to locals on Wednesday in Mrauk Oo town, 400 miles (640km) northwest of Yangon.

"They found the town almost deserted. It was later learned that the people had been ordered not to go out," he said. "But just before (the NLD leaders) left the town, about 20,000 people turned up. Policemen tried to prevent them but they could not stop the people from coming near her."

There were no reports of violence however and the police attempts appeared to have been restricted to pushing back the opposition supporters.

But it was one of the most serious signs of tension between the military and the NLD since UN brokered talks between the two sides started two years ago. Those talks have so far made little progress.

Suu Kyi, who won the 1991 Nobel Peace Prize, has been touring Rakhine state to drum up support for her pro-democracy cause. It was her fifth trip to provincial Myanmar, formerly known as Burma, since being released from 19 months of house arrest in May.

Her first few trips met no opposition from the authorities but a visit last month to Shan State in northeast Myanmar led to several reports of minor harassment by army and police, who appeared to be angered by the huge crowds she attracted.

Suu Kyi's Party won elections in 1990 by a landslide but has never been allowed to govern. The military, who have ruled for most of the last 40 years, say they want some form of democracy eventually but that the country is not yet ready for change.