Dhaka: Bangladesh has accused Myanmar of repeatedly violating its air space and warned that any more "provocative acts" could have "unwarranted consequences", raising the risk of a deterioration in relations already strained by the Rohingya refugee crisis.

Nearly 400,000 Rohingya Muslims from western Myanmar have crossed into Bangladesh since Aug. 25, fleeing a Myanmar government offensive against insurgents that the United Nations has branded a "textbook example of ethnic cleansing".

Bangladesh said Myanmar drones and helicopters had violated its air space three times - on Sept. 10, 12 and 14 - and it had called in a top Myanmar embassy official in Dhaka to complain.

"Bangladesh expressed deep concern at the repetition of such acts of provocation and demanded that Myanmar takes immediate measures to ensure that such violation of sovereignty does not occur again," the ministry said in statement late on Friday.

"These provocative acts may lead to unwarranted consequences."

A Myanmar government spokesman said he did not have information about the incidents Bangladesh had complained about but Myanmar had denied an earlier accusation.

The spokesman, Zaw Htay, said Myanmar would check any information that Bangladesh provided.

"Our two countries are facing the refugee crisis. We need to collaborate with good understanding," he told Reuters.

Bangladesh has for decades faced influxes of Rohingya fleeing persecution in Buddhist-majority Myanmar, where the Rohingya are regarded as illegal migrants.

Bangladesh was already home to 400,000 Rohingya before the latest crisis erupted on Aug. 25, when Rohingya insurgents attacked about 30 police posts and an army camp, killing a dozen people.

The Myanmar security forces and Rakhine Buddhist vigilantes responded with what rights monitors and fleeing Rohingya say is a campaign of violence and arson aimed at driving out the Muslim population.

Bangladesh has said all refugees must go home. Myanmar has said it will take back those who can verify their citizenship but most Rohingya are stateless.

Bangladeshi Prime Minister Sheikh Hasina was leaving on Saturday for the U.N. General Assembly where she would call for pressure to ensure Myanmar takes everyone back after stopping its "ethnic cleansing', her press secretary, Ihsanul Karim, told Reuters.

The conflict has led to a humanitarian crisis on both sides of the border and raised questions about Myanmar's path under the leadership of Nobel laureate Aung San Suu Kyi after nearly 50 years of strict military rule.

The generals still control national security policy but nevertheless, Suu Kyi has been widely criticised abroad for not stopping or condemning the violence.

There is little sympathy for the Rohingya in a country where the end of military rule has unleashed old animosities and the military campaign in Rakhine State is widely supported.

'STRONGHOLD'

U.N. Secretary-General Antonio Guterres and the U.N. Security Council have urged Myanmar to end the violence, which he said was best described as ethnic cleansing.

Ethnic cleansing is not recognised as a separate crime under international law but allegations of it as part of wider, systematic human rights violations have been heard in international courts.

Myanmar rejects the accusations, saying its security forces are carrying out clearance operations to defend against the insurgents of the Arakan Rohingya Salvation Army (ARSA), which claimed responsibility for the Aug. 25 attacks and similar, though smaller, attacks in October.

The government has declared ARSA a terrorist organisation and accused it of setting the fires and attacking civilians.

The ARSA says it is fighting for the rights of Rohingya and has denied links to foreign Islamists.

Myanmar's army chief, Senior General Min Aung Hlaing, said the violence - 93 clashes since Aug. 25 - was a bid by the insurgents to "build a stronghold", according to speech to officer trainees, posted on a military Facebook page.

More than 430 people have been killed, most of them insurgents, and about 30,000 non-Muslim villagers have been displaced, Myanmar has said. Human Rights Watch said satellite imagery showed 62 Rohingya villages had been torched.

The United States has called for the protection of civilians and a deputy assistant secretary of state, Patrick Murphy, is due in Myanmar next week.

China, which also vies for influence in Myanmar, joined a U.N. Security Council call for an end to the violence while its ambassador in Myanmar expressed his support for the government's action, Myanmar media reported.

Separately, the Committee to Protect Journalists has called on Bangladesh to release two Myanmar journalists detained last week while covering the refugee crisis. A police official told Reuters the two were found to be working on tourist visas and police were investigating.