More than 20 people have been killed in western Burma's Rakhine State, as international pressure mounts for an end to sectarian fighting between ethnic-Rakhine Buddhists and Rohingya Muslims.

President Thein Sein has declared a state of emergency and sent army troops in Rakhine, which has been hit with a wave of rioting and arson in recent days. Hundreds of homes have been destroyed.

U.S.-based Human Rights Watch said the violence is “spiraling out of control.” A Human Rights Watch official said there are reports riot police in the region are favoring the Rakhine over the Rohingya.

There was a heavy security presence Tuesday in the regional capital, Sittwe, where fires dotted the area and people ran to escape the chaos.

In predominately Muslim Bangladesh, officials say their border guards have turned back more than 500 Rohingya Muslims trying to flee the fighting. Bangladesh's Foreign Ministry says it is not in the the country's best interest to allow the Rohingyas in.

The violence erupted a week ago when a Buddhist mob in Sittwe ambushed a bus and killed 10 Rohingya passengers, mistakenly believing they were responsible for the recent gang-rape and murder of a Buddhist woman.

Lex Rieffel, a non-resident senior fellow at the U.S.-based Brookings Institution, told VOA this type of violence happens in several countries besides Burma.

“We've seen this kind of communal violence in many parts of the world. The country I deal a lot with Indonesia, and Indonesia has had some horrible episodes of communal violence and still this year continues to have horrible communal violence issues. Thailand, look at Thailand, southern Thailand. Look at the Philippines, (the island of) Mindanao, look at India. I mean this is hardly unique to Burma.”

The unrest has highlighted long-standing tensions between Buddhists and minority Rohingya Muslims. Burma does not classify its estimated 800,000 Rohingyas as Burmese citizens, instead regarding them as illegal immigrants from neighboring Bangladesh.

President Thein Sein has warned the violence could jeopardize the country's nascent reform process. He said the unrest is fueled by “hatred and revenge based on religion and nationality” and noted it could spread to other parts of the country. If that happens, he said the country's stability, peace, and democratization process could be severely affected.

Burma's military rulers transferred power to the new government last year. Rieffel of the Brookings Institution told VOA it is unclear how challenging the violence would be to Burma's new nominally civilian government.

“There's no simple answer to that question. I think we can only hope and pray that it's easy. That people sort of come to their senses and realize that there's no reason to … that there are other ways of dealing with differences than killing each other.”

U.S. Secretary of State Hillary Clinton has said she is deeply concerned about the situation. She has called for a transparent investigation into the violence and said the situation underscores the need for “serious efforts to achieve national reconciliation in Burma.”