The latest in a series of small bomb blasts has shaken one of the most prestigious hotels in Burma.
Police have detained three suspects over the explosion at the Traders Hotel in Rangoon which injured one guest.
The government says the explosions are an attempt by unknown individuals or an organisation to damage the country's image following the introduction of democratic reforms.
Opposition leader Aung San Suu Kyi said they were intended to create panic.
No group has claimed responsibility for the small but well co-ordinated explosions.
Small devices also exploded at a hotel in the northern part of the country - and at a pagoda in the same area - before dawn on Tuesday.
Police said that no-one was reported to have been injured in the blasts which took place in the Mandalay region.
On Friday a blast occurred at a guesthouse in central Burma and there were two more explosions in Rangoon on Sunday, reports say.
The BBC's Jonah Fisher in Bangkok says that with multiple armed groups harbouring decades of grievances, there is no shortage of candidates who may have carried out the bombings.
The hotel explosion, late on Monday, blew out a window in a guest's room, shooting shards of thick glass more than 30m (98ft) into the street in the city's central business district, according to the Associated Press.
Witnesses said that the room overlooked Sule Pagoda road, a main thoroughfare.
An American woman was taken to hospital with minor injuries. The US embassy said it was providing her with consular assistance.
The device was home-made, police say, and went off in the guest's bathroom.
"It was a time bomb. It was attached to a clock," a police official was quoted as saying by AFP news agency.
"The hotel management is working with the local authorities who are investigating this incident," said Phillip Couvaras, general manager of the hotel, which is popular with visiting officials and foreign tourists.
The bomb attacks are the latest violence in a year that has seen public euphoria over democratic reforms give way to sectarian attacks that have spread across Burma. Correspondents say that they have caused considerable public disquiet in Rangoon.
Opposition leader Aung San Suu Kyi told parliament that the devices were intended "to create panic".
"But the people should be cautious not to fall into the trap," she said, urging the authorities "urgently to expose the perpetrators".
The country has been hit by a string of bombings in recent years, which the government blames on separatist groups.
Two people were reported killed in Friday's blast at a guesthouse in Taungoo. One of the blasts in Rangoon injured three people, police said.
Speaking before the explosion at Traders hotel, Police Lt Gen Min Aung told AFP news agency that the system used "is the same in all the cases".
"We think an organisation or a person planted them all," he told the agency.
A spokesman for Burma's president told Radio Free Asia he believed the bombs were planted by those who wanted to damage the country's image as it assumed the chair of the Association of South-east Asian Nations (Asean).