Opponents of Burma's military regime have denied involvement in blasts on Saturday which left 11 dead in Rangoon.
The government blamed the attacks on insurgents
The bombs - at two busy supermarkets and a Thai trade fair - were the worst attacks of their kind in many years.
The junta quickly blamed three ethnic groups, as well as the self-proclaimed pro-democracy government in exile.
The Karen and Shan groups denied any involvement, while the opposition party - led by democracy icon Aung San Suu Kyi - condemned the violence.
The near-simultaneous blasts struck at about 1500 local time (0800 GMT) on Saturday.
According to the official New Light of Myanmar newspaper, the bombs had been hidden inside bags and triggered by timing devices.
Along with the 11 dead, more than 150 people were injured in the blasts that caused serious damage to the buildings, pictures on state TV showed.
Although one device exploded at the Thai trade fair, Thai Prime Minister Thaksin Shinawatra said he believed his nationals had not been explicitly targeted and that the matter was an internal Burmese affair.
A C-130 cargo plane flew into Burma on Sunday to bring home the 200-plus Thai nationals who were participating in the fair.
Security in Rangoon had been stepped up since a bomb blast at a market in the second city of Mandalay nearly two weeks ago.
Two women died and 13 people were hurt in that attack.
At the time, the military government blamed an unnamed group of insurgent destructive elements who, it said, wanted to disturb the stability of the country.
Burma has been ruled by a repressive military junta for the last decade and a half, prompting economic stagnation and international condemnation.
The junta has been led by three generals wielding almost absolute power.
But in-fighting and a lack of transparency have generated regular rumours of power struggles at the top.
On Sunday, those accused by the junta of involvement in the blasts suggested the military themselves may be involved.
"We don't know exactly who was behind it," said Sann Aung of the Thai-based National Coalition Government of the Union of Burma, which has led a government in exile since the military rejected Aung San Suu Kyi's 1990 election victory.
"The regime may have caused this bomb blast and then blamed the opposition," he said, quoted by the Reuters news agency.