By Prak Chan Thul
PHNOM PENH (Reuters) - Southeast Asian leaders will put pressure on Myanmar to resolve violence between Buddhists and minority Muslims, a senior regional official said on Sunday, after unrest left scores dead and as many as 100,000 people displaced since June.
Myanmar President Thein Sein has blamed nationalist and religious extremists for unrest in June and October that killed at least 167 people, but has faced criticism for failing to address underlying tensions in Rakhine State, where an estimated 800,000 Rohingya Muslims are not recognized as citizens.
"Eight hundred thousand people are now under tremendous pressure," Surin Pitsuwan, secretary-general of the Association of Southeast Asian Nations (ASEAN), told reporters on the sidelines of a regional summit in the Cambodian capital, Phnom Penh.
"If that issue is not handled well and effectively, there is a risk of radicalization, there is a risk of extremism," he said.
Surin said he expected ASEAN leaders to raise the issue with Myanmar, which is a member of the bloc, during bilateral talks. The leaders were committed to reducing internal conflicts as the group moves towards economic integration by 2015, he said.
After a week of violence in June killed at least 80 people in two townships, unrest in late October spread across much of the state. Witnesses said mobs of ethnic Rakhine Buddhists attacked Muslim villages with petrol bombs, swords and guns.
Nearly 4,700 homes were destroyed in 42 villages, according to government data compiled by U.N. agencies.
A Reuters investigation painted a troubling picture of organized attacks led by Rakhine nationalists tied to a powerful political party in the state, incited by Buddhist monks and, some witnesses said, abetted by local security forces.
More than 97 percent of the 36,394 people who fled the latest violence are Muslims, according to official statistics. Many now live in camps, joining 75,000 mostly Rohingya displaced in June. Others have set sail for Bangladesh, Thailand and Malaysia on rickety boats, two of which are reported to have gone down with as many as 150 people on board.
U.S. President Barack Obama is expected to raise the issue of ethnic tensions on Monday, when he travels to Myanmar and meets Thein Sein. Obama will be the first sitting U.S. president to visit Myanmar, also known as Burma.
Obama arrived in neighboring Thailand on Sunday.
"In addition to the democratic reforms, we've been concerned about the continued ethnic conflicts in Burma," Ben Rhodes, deputy national security adviser, told reporters accompanying Obama aboard Air Force One.
"I think the president will be underscoring that national reconciliation is also going to be a part of Burma's democratic transition," he said.
The United Nations said on Friday Thein Sein had sent a letter to Secretary-General Ban Ki-moon promising action to tackle the problems.
In a statement, Ban's office said Thein Sein had promised that "once emotions subside on all sides", his government was prepared to "address contentious political dimensions, ranging from resettlement of displaced populations to granting of citizenship".
It would also look at "issues of birth registration, work permits and permits for movement across the country for all, in line with a uniform national practice across the country ensuring that they are in keeping with accepted international norms". Many Rohingyas are subject to travel and work restrictions.
Rohingyas have lived for generations in Rakhine State, but Rakhines and other Burmese view them as illegal immigrants from neighboring Bangladesh who deserve neither rights nor sympathy.
Rakhines reject the term "Rohingya" as a modern invention, referring to them instead as "Bengali" or "kalar", a pejorative word for people of South Asian descent.
Many arrived as laborers from Bangladesh under British rule in the 19th century - grounds the government now uses to deny them citizenship. Rohingya were effectively rendered stateless under a 1982 Citizenship Law, which excluded them from a list of indigenous ethnic groups.
ASEAN groups Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Indonesia, Singapore, Thailand and Vietnam.
(Writing by Jason Szep; Editing by Alan Raybould and Robert Birsel)