By Aung Hla Tun

YANGON (Reuters) - Myanmar's president blamed nationalist and religious extremists for the violence between Muslims and Buddhists in Rakhine State in October that killed at least 89 people, and the United Nations said he had promised to address the underlying problems.

Thein Sein's remarks, in a meeting with Buddhists and Muslims carried by state television late on Friday and in a letter to the United Nations, came three days before U.S. President Barack Obama is due to visit the country, also known as Burma.

A Reuters investigation into a wave of sectarian assaults on Muslims in the state painted a 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.

The United States has suspended sanctions on Myanmar and removed an import ban in recognition of Thein Sein's political and economic reforms after half a century of military rule, but it still wants him to end ethnic conflict and release all political prisoners.

MRTV television said action had been taken against 1,081 people in connection with the violence in Rakhine, giving no details about those people or their offences.

"There were nationalist and religious extremists who incited and agitated improperly behind the scenes to spread the violence in the region," Thein Sein told the religious leaders.

"Besides, there were some foreign organizations and nations who tried to fuel the flame by circulating false and fabricated news," he said, without identifying them.

"The country will lose face among the international community if we fail to pursue the norms of human rights and humanitarian work being practised in many countries," he said, calling for concerted efforts by the government, Buddhist monks and people of all races and religion to work for a harmonious society where each could be respected.

LETTER TO THE U.N.

The United Nations said Thein Sein had sent a letter to Secretary-General Ban Ki-moon promising action to tackle the problems in Rakhine, home to an estimated 800,000 Rohingya Muslims that Myanmar does not recognize as citizens.

Many in Myanmar consider them to be illegal immigrants from neighboring Bangladesh, but Bangladesh does not recognize them as citizens, either.

In a statement issued late on Friday, 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.

The United Nations said Thein Sein had committed his government to meeting the humanitarian needs of people caught up in the violence and had said it would seek international assistance and cooperation.

It said he had condemned the "criminal acts" of elements inside his country and promised to deal with the perpetrators in accordance with the rule of law.

Ban, welcoming those steps, said the United Nations would work with Myanmar to help the affected people in Rakhine state and support measures needed "to comprehensively address the issues at the heart of the situation".

In the comments carried on television, Thein Sein said 167 people had been killed in two periods of violence in Rakhine in June and October this year, while 223 were injured. Some 101,000 buildings were destroyed and 111,000 people were made homeless.

At least 80 people died in the June violence. Some rights activists say the overall total for June and October could be much higher.

(Writing by Alan Raybould; Editing by Paul Tait)