Yangon: It was just before midnight when the crude time-bomb exploded in the ninth-floor guest room in the luxurious Traders Hotel in Myanmar’s biggest city, badly wounding an American tourist and showering the streets below with glass.

A police source told Reuters the explosion late on Monday was part of a coordinated series of bomb attacks across Myanmar by an “organised group”, targeting tourist haunts, a Buddhist temple and other public places. It was the seventh blast since Friday and was followed by two more explosions early on Tuesday.

Soon after the bomb went off at the Traders in Yangon, another device exploded in the parking lot of the Shwe Pyitsone Hotel in Sagaing region and another at a pagoda, Sagaing police and a government official said. There were no casualties.

The bomb attacks are the latest violence in a year that has seen the euphoria over democratic reforms give way to sectarian attacks that have spread across Myanmar, also known as Burma.

Anti-Muslim unrest simmered under the military junta that ran the Buddhist-dominated country for nearly half a century.

But the worst has occurred since the quasi-civilian government took power in March 2011.

Police and diplomatic sources, however, said it was not clear if the blasts were connected to religious unrest.

“I think these blasts and aborted attempts were carried out by a systematically organised group,” said a police official in Yangon who declined to be identified because he is not authorised to speak to the media.

“By the look of the devices they used, and the way they carried it out, they must have been trained in terrorist acts systematically.” He said devices found in Mandalay and Yangon recently were made in the same way, with hand-grenades.

Police are already investigating the series of bombings that began on Friday, when an explosion killed two people in a guesthouse in the town of Taungoo, about 55km (35 miles) from the capital, Naypyitaw.

There are few hotels with as much symbolic significance in Yangon as the 22-storey, 334-room Traders, owned by billionaire Robert Kuok’s Shangri-La Asia Ltd. It is a hive of activity; businessmen, journalists, tourists and aid workers mingle in its lobby.

Until this year, several U.N. agencies had offices there.

“To alarm and destabilise”

According to a Reuters witness and police, the bomb in the Traders appeared to go off in the bathroom in a room overlooking Sule Pagoda road, a main thoroughfare.

“It sounded like a subdued explosion,” said Graeme Romer, a guest staying on the eighth floor.

He said he went downstairs to the lobby and saw an injured woman wrapped in sheets lying on the floor. “She was bleeding profusely,” Romer said. The woman was on holiday with her husband and two children who were not injured.

Two bombs exploded in Yangon on Saturday, according to police, one at a bus stop that caused no injuries and another that slightly wounded two boys. Police said they found an unexploded bomb in a Yangon restaurant on Monday.

Police said they had arrested four suspects in connection with the bomb attacks, including one identified as Saw Myint Lwin, 26. He was seen on closed-circuit television cameras at the Traders and arrested in Mon State, police said.

“These devices were obviously not intended to cause large numbers of casualties,” said Anthony Davis, an analyst at IHS-Jane’s, a global security consulting firm. “They were designed to alarm and destabilise. And their geographical spread reinforces that.” Presidential spokesman Ye Htut linked the blasts to Myanmar assuming this year’s chairmanship of the Association of Southeast Asian Nations (Asean).

“It must have been carried out to create worries and concern among the people and to make the international community doubt the security standard in Myanmar at a time when Myanmar is going to take the Asean chair,” Ye Htut told Radio Free Asia’s Burmese-language service.

Myanmar has been hit by bombings before. Three explosions during a traditional new year festival in 2010 killed at least 10 people. In 2005, three bombs at a convention centre and markets killed 23 people.

Authorities blamed the 2005 bombing on ethnic rebel groups and a government in exile.

A Southeast Asian diplomat in Yangon cast doubt on the involvement of ethnic rebels this time. “I think there could be a connection with some group outside the country.”