Nobel Peace Prize winner and the de facto leader of Myanmar Aung San Suu Kyi has a "last chance" to stop its army that is forcing hundreds and thousands of Rohingya to flee abroad, said United Nations.
United Nations Secretary-General Antonio Guterres told BBC that unless she acted now, the tragedy will be absolutely horrible.
The UN has previously said the offence could amount to ethnic cleansing.
According to Myanmar, it is responding to last month's deadly attacks by militants and denies it is targeting civilians.
The military launched its "operation" after the attacks on police in the northern Rakhine state of Myanmar.
In an interview with BBC's HARDtalk programme ahead of this week's UN General Assembly, the UN chief said Aung San Suu Kyi had a last chance to stop the offensive during her address to the nation on Tuesday, reports BBC.
"If she does not reverse the situation now, then I think the tragedy will be absolutely horrible, and unfortunately then I don't see how this can be reversed in the future," the UN chief added.
He also said it was clear that Myanmar's military still has the upper hand in the country, putting pressure to do what is being done on the ground in Rakhine, reports BBC.
Aung San Suu Kyi, who spent many years under house arrest in the junta-run Myanmar, is now facing growing criticism over the Rohingya issue.
She recently denied to attend the UN General Assembly in New York and claimed that the crisis is being distorted by a huge iceberg of misinformation.
Tensions were being fanned by fake news promoting the interests of terrorists, she said.
The UN chief's warning comes after Bangladesh said it was now limiting the movement of more than 400,000 Rohingya who have fled from Myanmar.
According to Bangladesh police, Rohingya would not be allowed to travel anywhere outside of their allocated homes, not even to live with family or friends.
Transport operators and drivers have also been urged not to carry refugees, with landlords told not to rent out any property to them.
Bangladesh also announced plans to build shelters for up to 400,000 people near the city of Cox's Bazar.
On August 25, Rohingya militants attacked police posts in northern Rakhine which left 12 security personnel dead.
Rohingya who have fled Myanmar since then say the military responded with a brutal campaign, burning villages and attacking civilians in a bid to drive them out.
A new Human Rights Watch report released on Friday accused the Myanmar military of an ethnic cleansing campaign and detailed scores of villages targeted with arson attacks.
Myanmar officials blame the Rohingya insurgents for the violence, with government spokesman Zaw Htay urging displaced people to find refuge in temporary camps set up in Rakhine state.
Htay said Myanmar would not be able to allow all those who fled to Bangladesh to return.


