The situation in Myanmar is a "textbook example of ethnic cleansing", United Nations Human Rights Chief Zeid Ra'ad Al Hussein told the UN Human Rights Council on Monday, as the number of Rohingya Muslims fleeing the country for Bangladesh topped 300,000.
The UN human rights chief accused Myanmar of waging a "systematic attack" on the Rohingya Muslims and warned that "ethnic cleansing" seemed to be under way.
"Because Myanmar has refused access to human rights investigators the current situation cannot yet be fully assessed, but the situation seems a textbook example of ethnic cleansing," he told the UN forum.
Suu Kyi, a Nobel peace laureate, has come in for strong international criticism over the military crackdown on the Rohingya, which began when militants ambushed security forces on August 25.
Dalai Lama calls on Suu Kyi for peaceful end to Rohingya crisis
The Dalai Lama joined on Monday fellow Nobel peace laureates Malala Yousafzai and Archbishop Desmond Tutu in urging Suu Kyi to intervene on behalf of the Rohingya Muslims.
The UN special rapporteur on human rights in Myanmar said the latest violence may have left more than 1,000 dead, most of them Rohingya.
A further 27,000 ethnic Rakhine Buddhists as well as Hindus have also fled violence that has gripped northern Rakhine, where international aid programmes have been severely curtailed.
The Dalai Lama expressed concerns about violence and urged Suu Kyi to "reach out to all sections of society" to try to resolve the crisis in Rakhine, where the Rohingya, a stateless Muslim minority, have endured decades of persecution.
"Questions that are put to me suggest that many people have difficulty reconciling what appears to be happening to Muslims there with Myanmar's reputation as a Buddhist country," he wrote in the letter.
"I appeal to you and your fellow leaders to reach out to all sections of society to try to restore friendly relations throughout the population in a spirit of peace and reconciliation."
"If the political price of your ascension to the highest office in Myanmar is your silence, the price is surely too steep," said Tutu, who became the moral voice of South Africa after helping dismantle apartheid there.
Myanmar's population is overwhelmingly Buddhist and there is widespread hostility toward the Rohingya Muslims, who are denied citizenship and labelled illegal "Bengali" immigrants.
Buddhist nationalists, led by firebrand monks, have operated an Islamophobic campaign calling for them to be pushed out of the country.
The Dalai Lama said he had spoken to Suu Kyi in the past about religious tensions in her country and was urging her again to curb the violence.
"As a fellow Buddhist and Nobel laureate I am appealing to you and your colleagues once more to find a lasting and humane solution to this festering problem," he wrote.