Attempts to disrupt campaigning for Burma's historic by-elections tomorrow are "beyond acceptable", opposition leader Aung San Suu Kyi said yesterday, in her first public appearance since falling ill last weekend.

"What has been happening in this country is really beyond what is acceptable for a democratic election. Still, we are determined to go forward because we think that is what our people want," a frail but defiant Mrs Suu Kyi, 66, said.

She accused her rivals of vandalising election posters, padding electoral registers and "many cases of intimidation", including two attempts to injure candidates with projectiles.

The US and European Union have hinted economic sanctions could be lifted if the election is free and fair.

The vote needs the blessing of Ms Suu Kyi. She is contesting one seat in her first election since being freed from house arrest in 2010.

Her National League for Democracy (NLD), competing for 44 of the 45 by-election seats, has complained of irregularities that could undermine the vote.

Burma's size, energy resources and ports have made it a vital energy security asset for China's western provinces, and a priority for Washington.

"There have been cases of vandalism of NLD signboards and posters and many, many cases of intimidation," said Ms Suu Kyi.

After 49 years of isolation and often brutal army rule, Burma has limited experience in holding ballots. The 2010 election was widely seen as rigged to favour the Union Solidarity and Development Party. But most diplomats say they believe Burma's rulers are sincere.

The NLD claims the president, who is supposed to be impartial, has tried to influence the vote.