Myanmar's military has ended a clearance operation in the country's troubled Rakhine State, government officials said, ending a four-month sweep that the United Nations said may amount to crimes against humanity and possibly ethnic cleansing.

The security operation had been under way since nine policemen were killed in attacks on security posts near the Bangladesh border on October 9. Almost 69,000 Rohingyas have since fled from Myanmar to Bangladesh, according to UN estimates.

The violence has renewed international criticism that Myanmar leader Aung San Suu Kyi has done too little to help members of the Muslim minority.

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The government led by Nobel laureate Suu Kyi has denied almost all allegations of human rights abuses in Rakhine, including mass killings and gang rapes of Rohingya Muslims, and said the operation was a lawful counterinsurgency campaign.

"The situation in northern Rakhine has now stabilised. The clearance operations undertaken by the military have ceased, the curfew has been eased and there remains only a police presence to maintain the peace," newly-appointed national security advisor Thaung Tun was quoted as saying in a statement released by State Counselor's Office late on Wednesday.

"There can be no excuse for excessive force, for abuses of fundamental human rights and basic criminality. We have shown that we are ready to act where there is clear evidence of abuses," he told a group of diplomats and UN representatives in a meeting, according to the statement.

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Two senior officials from Myanmar's President Office and the Ministry of Information confirmed that the army operation in northern Rakhine had ended but said the military force remained in the region to maintain "peace and security".

Myanmar military did not immediately respond to requests for comments.

The military and police have separately set up a team to investigate alleged crimes after Suu Kyi promised to probe UN allegations of atrocities against the Muslim minority.

More than 1,000 Rohingya Muslims may have been killed in the crackdown, two senior UN officials dealing with refugees fleeing the violence told Reuters last week.

A Myanmar presidential spokesman has said the latest reports from military commanders were that fewer than 100 people had been killed in the counterinsurgency operation.

Rohingya Muslims have faced discrimination in Buddhist-majority Myanmar for generations. They are regarded as illegal immigrants from Bangladesh, entitled only to limited rights and some 1.1 million of them live in apartheid-like conditions in northwestern Myanmar.