YANGON, Myanmar — Two bombs exploded Sunday in the largest city of the military-ruled country, witnesses said, but no casualties were immediately reported.

The witnesses, who spoke on condition of anonymity for fear of official reprisal, said the first blast occurred on a downtown Yangon street at around 8 p.m. The second blast occurred about an hour later on a different street near the luxurious Traders Hotel, they said.

No further details were immediately available, and there were no immediate claims of responsibility. The government has not blamed any group.

The roads were immediately blocked off by security and riot police.

A car was damaged in the first blast and residents heard a loud noise, eyewitnesses said. Some witnesses said a small bomb was hidden underneath the car. Residents in the area said the second blast also came from underneath a car.

The United Nations estimates at least 31 people were killed and thousands more detained in September when Myanmar's government crushed peaceful pro-democracy demonstrations.

Myanmar, also known as Burma, has been in a political stalemate since 1990 when Nobel Peace Prize laureate Aung San Suu Kyi's National League for Democracy party won a general election but was not allowed to take power by the military, which continues to tightly control the country.

Suu Kyi, who is currently under house arrest, has been in detention without trial for more than 12 of the past 18 years.

The military junta announced in February that it will hold a constitutional referendum in May and a general election in 2010. It marks the first time since the 1990 elections that Myanmar's people have been allowed any kind of vote.