BANGKOK (AFP) - Myanmar local security forces killed Muslim villagers and assaulted people trying to flee a fresh outbreak of sectarian violence in western Rakhine state last month, a rights watchdog said Sunday.

Local forces killed ethnic minority Kaman Muslims in the town of Kyauk Pyu while government troops “stood by and watched”, according to New York-based Human Rights Watch (HRW).

Soldiers from the local border guard force meanwhile “severely beat” dozens of displaced Rohingya Muslims arriving by boat near the Rakhine state capital Sittwe from violence-hit local villages, it said.

Elsewhere, however, security forces provided protection to displaced Rohingya and Kaman Muslims by firing shots in the air to fend off Buddhist mobs and by providing water and food, according to HRW.

Two major outbreaks of violence between Muslims and Buddhists in Rakhine since June have left 180 people dead and more than 110,000 displaced. Most of the displaced were Rohingya, a minority group that has faced decades of discrimination.

HRW released new satellite imagery which it said showed extensive destruction of homes and other property in three mainly Rohingya areas.

It reported accounts of “gruesome casualties” on both sides of the Buddhist-Muslim clashes, including beheadings and killings of women and children.

“The satellite images and eyewitness accounts reveal that local mobs, at times with official support, sought to finish the job of removing Rohingya from these areas,” said Brad Adams, the watchdog’s Asia director.

He urged US President Barack Obama to press Myanmar’s reformist leader Thein Sein on the issue when he makes a historic visit to Yangon on Monday following sweeping political changes in the former pariah state. “The absence of accountability for this horrific violence gives a green light to extremists to continue their attacks and abuses,” Adams said.

Meanwhile, Asean chief Surin Pitsuwan said on Sunday that Rohingya Muslims in western Myanmar were the victims of “disturbing” ethnic violence, but stopped short of calling the bloodshed genocide.

“I would call it a disturbing trend of ethnic violence that could become destabilising to the region,” Surin told AFP in Phnom Penh at a summit of the 10-member Association of Southeast Asian Nations.

“I have already given out a warning that it could be radicalised. That would not be good to anybody in the region.”

But Surin did not endorse a statement from the Organisation of Islamic Cooperation, which on Saturday called the Rohingya victims of “genocide”.

“I think the statement by the OIC reflects the frustration... of 57 countries,” Surin said when asked whether he would call the violence “genocide”. “This is a very very, frustrating, worrisome situation.”

Meanwhile, President Barack Obama flexed US power in Asia Sunday on a regional tour that will make history when he lands in Myanmar, calling on its leaders to step up their startling political reform drive. Obama touched down in Air Force One in Bangkok, sending a message that relationships like the six-decades-old treaty alliance with Thailand will form the bedrock of US diplomacy as the region warily eyes a rising China.

Obama will on Monday become the first sitting US president to visit formerly isolated Myanmar. He will praise President Thein Sein for ending a dark era of junta rule, but also prod him to go much further towards genuine democracy.

Speaking in Thailand on the eve of the visit, Obama praised Myanmar’s reforms but urged the regime to do more. “President Thein Sein is taking steps that move us in a better direction,” he told a press conference.

“But I don’t think anybody’s under any illusion that Burma’s arrived,” he added, using the country’s former name.

“The country has a long way to go. I’m not somebody who thinks that the United States should stand on the sidelines and not want to get its hands dirty when there’s an opportunity for us to encourage the better impulses inside a country.”

“What a peaceful place,” US Secretary of State Hillary Clinton told the president, who remarked that they were having a “treat” because the normally crowded tourist attraction had been cleared for their visit.

Then Obama called at Siriraj hospital in Bangkok for an audience with revered King Bhumibol Adulyadej, seen as a symbol of continuity for a kingdom with a turbulent political past.

Obama and Clinton greeted and shook hands with the frail monarch, who turns 85 next month.

After talks with Thai Prime Minister Yingluck Shinawatra focusing on trade, regional politics, counter-narcotics issues and terrorism, Obama held a joint press conference with her.

His visit to Asia, coming just 12 days after he won re-election, is the latest manifestation of his determination to anchor the United States in a dynamic, fast-emerging region he sees as vital to its future.