The head of the Red Cross on Sunday said it was not safe to return Rohingya refugees to their homes in Myanmar, where he described whole villages abandoned and destroyed.
Peter Maurer toured strife-torn western Myanmar before visiting refugee camps over the border in neighbouring Bangladesh, where nearly one million Rohingya have sought refuge from violence.
The bulk of the persecuted Muslims in Bangladesh have arrived since August, fleeing a huge Myanmar army crackdown in troubled Rakhine state that the UN has likened to ethnic cleansing.
UN Secretary-General Antonio Guterres on Monday will make his first visit to the camps since that influx of nearly 700,000 Rohingya sparked a humanitarian crisis in southeast Bangladesh.
The UN says Guterres, who discussed the Rohingya with Bangladesh Prime Minister Sheikh Hasina in Dhaka on Sunday, will use the trip to study prospects for "a safe, voluntary and dignified return" of refugees to Myanmar.
But relief agencies warn that conditions in Rakhine, which is heavily restricted to international observers, remain too unsafe to consider repatriating the Rohingya to Buddhist-majority Myanmar.
Maurer, the president of the International Committee of the Red Cross, said a lot more was needed to improve the situation he witnessed in Rakhine during an official visit the past few days.
"What I've seen in terms of destruction of villages, abandonment of situations, disruptions in markets, of livelihood, of communities, I don't think the present moment is an ideal condition to return," Maurer told AFP in an interview in Chakmarkul refugee camp.
He said more was needed for those families eking out survival in gigantic tent cities in Bangladesh, where many would rather endure hardship than return to persecution.
"We need to prepare the ground for returns for those who wish to return," Maurer said.
Bangladesh and Myanmar agreed in November to begin repatriating the Rohingya but the process has stalled, with both sides accusing the other of frustrating the effort.
Fewer than 200 have been resettled, and the vast majority refuse to contemplate returning until their rights, citizenship and safety are assured.
The Rohingya are loathed by many in Myanmar, where they were stripped of citizenship and branded illegal immigrants from Bangladesh despite calling Rakhine their homeland.
The UN has says conditions in Rakhine are not ripe for a safe, voluntary and dignified repatriation, but signed an agreement with Myanmar to assess conditions on the ground to help refugees make an informed decision.
The UN Security Council visited Myanmar and Rakhine state in early May, meeting with refugees who gave detailed accounts of killings, rape and torching of villages at the hands of Myanmar's military.
Myanmar has vehemently denied allegations by the US, United Nations and others of ethnic cleansing.