Bangladesh has accused Myanmar of repeatedly violating its air space and warned that anymore “provocative acts” could have “unwarranted consequences”, raising the possibility of a deterioration in relations already strained by a 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 a 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.

“At this time, our two countries are facing the refugee crisis. We need to collaborate with good understanding,” Zaw Htay told Reuters.

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

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 responded with what rights monitors and fleeing Rohingya say is a campaign of violence and arson aimed at driving out the Muslim population.