A spokesman for the United Nations, Martin Nesirky, says President Thein Sein's remarks were made in a letter to the UN Secretary-General, Ban Ki-moon.
In the letter, President Thein Sein also promised to bring the perpetrators of the violence in western Burma to justice.
"The president condemned the 'criminal acts' of elements inside his country that caused the 'senseless violence' that resulted in widespread loss of life, destruction of property and displacement of families in the Rakhine State," Mr Nesirky said.
"He promised to deal with the perpetrators in accordance with the rule of law."
President Thein Sein's letter comes as the reformist leader faces criticism from the United Nations and Muslim countries over its treatment of stateless Rohingya Muslims.
More than 100,000 people have been displaced in Burma since June in two major outbreaks of violence in Rakhine state between the Rohingyas and Buddhists.
Dozens have been killed on both sides and thousands of homes torched.
President Thein Sein says 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."
The UN says President Thein Sein has met Buddhist and Muslim community leaders on Friday and "strongly called" on them "to exert maximum effort to foster harmony and cooperation between the communities."
Mr Ban has welcomed the letter and meeting "as positive steps in the right direction," said the UN spokesman.
He said the assurances made by President Thein Sein "would be carefully noted by the international community."
The Burmese leader has asked for international assistance and Mr Ban says the UN will work closely with the government to help victims in Rakhine state.
Rohingyas, a Muslim minority who speak a Bengali dialect in mainly Buddhist Burma, claim decades of persecution.
The government views the roughly 800,000 Rohingya in Rakhine as illegal Bangladeshi immigrants and denies them citizenship.
Decades-old animosity between Buddhists and Rohingya exploded in June after the apparent rape and murder of an ethnic Rakhine woman sparked a series of revenge attacks.
In the United States, officials say President Barack Obama is expected to lift more sanctions during his landmark visit to Burma on Monday.
A Congressional aide says Mr Obama will announce the US will remove its current ban on most imports from Burma.
The aide says the Obama administration is also expected to expand a list of companies in Burma with which US firms are barred from doing business.
Meanwhile, the US Secretary of State, Hillary Clinton, says strong economic pressure can convince military regimes like Burma to reform.
Speaking at a university in Singapore, Ms Clinton says countries like North Korea and Iran should take note.
She says a combination of economic sanctions and the benefits of rejoining the global economy is what's spurred Burma's government to take action.
"The United States is responding not just with growing diplomatic engagement, but also with new economic ties that we believe will help encourage further political and market reforms."