An explosion that injured a foreign guest in one of the most prestigious hotels in Myanmar's main city was caused by a small, homemade time bomb placed in her room, police said Tuesday.

It was one of a series of unexplained recent explosions in the country, and the government alleged that the perpetrators were trying to tarnish the country's new image.

Police Officer Myint Htwe said three suspects were detained in relation to the blast late Monday at the Traders Hotel in the heart of Yangon that wounded a 43-year-old American and blew out the window of her 9th floor room. Her husband and two young children were not harmed.

It was the most high-profile of the recent blasts, including two before dawn Tuesday in the region of Mandalay. Few details were available about the others. One media report said the blasts have killed at least two people and several others have been wounded.

Small bombings occurred frequently when Myanmar was under 50 years of brutal military rule, most often blamed on armed exiled groups or ethnic rebels.

But they have become rare since the nominally civilian government of President Thein Sein took office in 2011, made sweeping reforms and ended the house arrest of Nobel laureate Aung San Suu Kyi, who became the opposition leader in Parliament.

The government alleged that an unidentified person or group may be committing the attacks to tarnish the country's new, improved image.

"These are deliberate acts to create panic, but the people should be cautious not to fall into the trap," Suu Kyi told reporters in the capital, Naypyitaw. She said it's very important for authorities "to urgently expose the perpetrators."

The explosion at the 22-story Trader's Hotel shot shards of thick glass more than 30 meters (yards) into the street, but the building exterior showed no other damage. The device apparently was in the bathroom, scattering towels, toiletries and a red purse across the entrance way floor. A chair was overturned and part of the wooden wardrobe lifted off its hinges and was lying on the ground.

Witnesses saw blood on the injured woman's arm and below her waist as she was escorted through the lobby by her husband and was taken to a Yangon hospital. The children, aged 5 and 7, were sleeping in another room and did not witness the blast.

"Our consular officers in Rangoon (Yangon) have visited the U.S. citizen and are providing appropriate consular assistance," said a U.S. Embassy official, refusing further comment due to privacy considerations.

A dozen police and heavily armed soldiers with a sniffer dog entered the glitzy hotel soon after the explosion. Later, many of them crowded into the destroyed room, blocked off with yellow security tape, to inspect the damage.

Traders' general manager Phillip Couvaras said in a statement that the hotel, part of the Shangri-La group, was working with authorities to investigate what happened and would not comment further because it was an active police investigation.

Despite the rapid changes in Myanmar since 2011, many activists and rights groups say it is still far from free and dissent is frequently stifled despite reforms.

Thein Sein's government has struggled to end a civil war with Kachin rebels and curb rising anti-Muslim violence that has killed hundreds of minority Muslims and displaced nearly 150,000 more in the predominantly Buddhist country since last year.

Presidential spokesman, Ye Htut, told Radio Free Asia the recent bombings may be aimed at smearing the country's image.

"I think that the explosions may have been timed to coincide with Myanmar becoming the chair of ASEAN," he told RFA Myanmar's service, referring to the regional grouping.

The country of 60 million is also preparing to host the Southeast Asian Games, the region's largest sports event, after a 44-year hiatus, he noted.

"Someone or some organization" wants to "make the international community misunderstand the situation of stability and peace in Myanmar," he said.

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Associated Press writers Aye Aye Win, Esther Htusan and Todd Pitman contributed to this report.