YANGON (AFP) - Myanmar police said Tuesday a makeshift bomb caused a blast at a luxury Yangon hotel that wounded an American woman, as they questioned several suspects following a series of explosions.

Officials voiced fears that the incidents could be aimed at derailing democratic reforms as the country prepares to host a major regional sporting event in December and chair the Association of Southeast Asian Nations (ASEAN) next year.

The American woman was taken to hospital with wounds to her thigh and her hand after the blast ripped through a guest room where she was staying at the Traders Hotel in central Yangon late on Monday, police said.

"It was a time bomb. It was attached to a clock," said a police official who visited the scene.

Officials said they detained a 27-year-old suspect early Tuesday in the southeastern state of Mon. He had previously stayed in the hotel room where the blast occurred.

"A case was opened against him with two charges of breaking the explosives act and causing serious harm to others," the police official said.

Opposition leader Aung San Suu Kyi urged people to remain calm.

"These acts are intentionally instigated against the people. So we should not fall into their trap," she told reporters in Naypyidaw.

The U.S. Embassy in Yangon said it was providing consular assistance to the wounded woman but declined to give any further information. Police said her condition was improving.

Military officials and soldiers with sniffer dogs were seen at the Traders Hotel following the blast while shattered glass covered the road outside.

The hotel, part of the Shangri-La group, is located in the heart of Myanmar's commercial hub. It is popular with foreign tourists and visiting business people.

Police said two other suspects had been detained for questioning in connection with a string of mysterious explosions.

A man and a woman were killed and another person injured in an explosion Friday at a guesthouse in the town of Taunggu, about 65 kilometers from the capital Naypyidaw, police said.

Two other devices exploded in Yangon on Sunday -- one at a bus stop and another under a truck, which wounded two teenagers.

Two more makeshift devices were found in the cities of Yangon and Mandalay on Monday while two blasts were reported early Tuesday at a restaurant and near a pagoda in the northwestern region of Sagaing.

Bomb blasts were relatively common under the former junta, which usually blamed the explosions on armed exile groups or ethnic rebels.

In the last major attack, three bombs rocked a park in Yangon in April 2010 as thousands of revellers celebrated an annual water festival, leaving 10 people dead and dozens wounded.

But such explosions had been rarer under a new quasi-civilian government which took power in 2011 promising political reforms and efforts to end long-running ethnic insurgencies.

The recent bombs were small, essentially "low-tech" devices and so not intended to cause large-scale casualties, said Anthony Davis, security analyst with consulting firm IHS-Jane's.

He said the blasts were clearly coordinated and "designed to cause alarm and destabilize the country".

"It is frankly difficult to see how either a foreign terrorist group or domestic ethnic insurgents in -- or negotiating -- cease-fire arrangements with the government might benefit from this sort of low-level destabilisation," he told AFP.

President Thein Sein's government has reached tentative peace deals with major ethnic minority rebel groups as part of political reforms that have led to the lifting of most Western sanctions and prompted an influx of foreign tourists.

Experts say the pace of the reforms appears to have unsettled some regime hardliners.

The nation has also been hit by several outbreaks of Buddhist-Muslim religious violence since June 2012 that have left about 250 people dead and more than 140,000 homeless.

Presidential spokesman Ye Htut said the recent bombs were intended to spread fear.

"I think that the explosions may have been timed to coincide with Myanmar becoming the chair of ASEAN and getting ready to host the Southeast Asian Games, to make the international community misunderstand the situation of stability and peace in Myanmar," he told Radio Free Asia.