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 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.

"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 on suspicion of breaking the explosives act and causing serious harm to others. He had previously stayed in the hotel room where the blast occurred.

An unnamed source from armed ethnic rebel group the Karen National Union (KNU) told AFP that the man was one of its members, adding that he could have been trying to show "dissatisfaction" with a tentative ceasefire deal between the rebels and the reformist government.

The KNU leadership in Thailand denied responsibility, and group vice president Naw Zipporah Sein said she was "concerned" by reports of the explosions.

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

But such explosions have been rarer under the new quasi-civilian regime which took power in 2011.

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 and factions in the rebel organisations.

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 US Embassy in Yangon, which said there was currently "no indication" that Americans were specifically targeted, was providing consular assistance to the wounded woman.

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 popular with foreign tourists and business people and is located in the heart of Myanmar's commercial hub.

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

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 kilometres (40 miles) from the capital Naypyidaw.

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

Another two 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.

Anthony Davis, security analyst at IHS-Jane's, said the blasts were coordinated and "designed to cause alarm and destabilise the country", but were small, "low-tech" devices and so not intended to cause large-scale casualties.

"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.

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.

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.