At least 31 people died when troops suppressed protests last year
An explosion in the centre of Burma's largest city, Rangoon, has injured at least four people.
The incident happened a day before the first anniversary of the bloody military crackdown on major anti-government protests.
The city is currently under tight security ahead of the anniversary.
The UN has confirmed that 31 people were killed when the 2007 protests were put down, but activists insist the death toll was much higher.
Hundreds of protesters are still thought to be in detention, including some key dissidents.
Analysts say there are unlikely to be any significant demonstrations to mark the anniversary inside Burma, although many events are being planned outside the country.
The bomb went off at a bus stop outside City Hall in the centre of Rangoon, police officials told reporters.
It is the latest in a series of blasts, which the government usually blames on underground dissidents or ethnic rebels.
On 11 September, two people were killed and another 10 wounded by two explosions at a video cafe northeast of Rangoon, state media reported.