Police in Myanmar said Monday they were investigating a series of mysterious bomb blasts that have left two people dead and several wounded in recent days.
A man and a woman were killed and another person was injured in an explosion Friday at a guesthouse in the town of Taunggu about 65 kilometres (40 miles) 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, according to the authorities.
Two more makeshift devices were found in the cities of Yangon and Mandalay on Monday.
"We cannot say who is responsible for these acts," said Police Lieutenant General Min Aung of the Myanmar Police Force's intelligence and security department.
"We're still investigating. The system they used is the same in all the cases. We think an organisation or a person planted them all," he told AFP by telephone from Naypyidaw.
He said security had been stepped up in Yangon.
Bomb blasts were relatively common under the former junta, which usually blamed the explosions on armed exile groups or ethnic rebels.
But such explosions are less common under a new quasi-civilian government which took power in 2011, promising political reforms and efforts to end long-running ethnic insurgencies.
In a message posted on its official Facebook page, the Yangon police appealed to people to be vigilant for any suspicious objects at railway stations, bus stops and other public places.
"We also urge people to cooperate to find those causing unrest and casualties with explosions," it said.
President Thein Sein's reformist government has reached tentative peace deals with the major ethnic minority rebel groups in the country, which has been racked by civil wars since independence from Britain in 1948.
But the nation has been rocked by several outbreaks of Buddhist-Muslim religious violence since June 2012 that has left about 250 people dead and more than 140,000 left homeless, mostly Muslims.