Nobel Prize Laureate Archbishop Emeritus Desmond Tutu has spoken up strongly against his one-time friend and fellow prize winner Aung San Su Kyi for her handling of the Rohingya crisis in Myanmar.

"I am now elderly, decrepit and formally retired, but breaking my vow to remain silent on public affairs out of profound sadness about the plight of the Muslim minority in your country, the Rohingya," wrote Tutu in an open letter to the Myanmar leader.

"For years I had a photograph of you on my desk to remind me of the injustice and sacrifice you endured out of your love and commitment for Myanmar's people."

Suu Kyi was feted for her years of peaceful opposition to Myanmar's junta rulers, but is now being urged to speak up for the Rohingya, with Muslim nations and the UN leading condemnation of her government.

Tutu's Sept. 7 letter came as the UN migration agency, the IOM and the UN refugee agency UNHCR both said that 270,000 people have fled violence in Myanmar to seek safety in Bangladesh in two weeks.

The spokesperson for the UNHCR, Duniya Aslam Khan, issued a call for "urgent action" amid "a dramatic increase in the number of refugees fleeing violence in Myanmar's Northern Rakhine state" during a UN briefing.

"The Rohingya are a stateless Muslim minority in Myanmar who have faced discrimination and extreme poverty for decades," said Khan.

"They have not been allowed to exercise their basic rights including the freedom to move, right to education, work and other social, civil and political rights.

"The Rohingya fleeing Myanmar are now stateless refugees, making them even more vulnerable and adding more challenges to the search for solutions.

"The Rohingya fleeing Myanmar are now stateless refugees, making them even more vulnerable and adding more challenges to the search for solution," said the UNHCR spokesperson.

"While most of Rohingya refugees arrive on foot, mostly walking through the jungle and mountains for several days, thousands are braving long and risky voyages across the rough seas of the Bay of Bengal."

Khan said the Rohingya's wait on the Myanmar border to take fishing boats to Teknaf in Bangladesh.

"The vast majority are women including mothers with newborn babies, families with children. They arrive in poor condition, exhausted, hungry and desperate for shelter."

Tutu's letter noted than in 2010 he rejoiced at Suu Kyi's freedom from house arrest, and in 2012 at her election as leader of the opposition.

"Your emergence into public life allayed our concerns about violence being perpetrated against members of the Rohingya.

'ETHNIC CLEANSING'

"But what some have called 'ethnic cleansing' and others 'a slow genocide' has persisted – and recently accelerated. The images we are seeing of the suffering of the Rohingya fill us with pain and dread.

"We know that you know that human beings may look and worship differently – and some may have greater firepower than others – but none are superior and none inferior; that when you scratch the surface we are all the same, members of one family, the human family; that there are no natural differences between Buddhists and Muslims; and that whether we are Jews or Hindus, Christians or atheists, we are born to love, without prejudice.

"Discrimination doesn't come naturally; it is taught," said Tutu.

"My dear sister: If the political price of your ascension to the highest office in Myanmar is your silence, the price is surely too steep.

"A country that is not at peace with itself, that fails to acknowledge and protect the dignity and worth of all its people, is not a free country."

Tutu said, "As we witness the unfolding horror we pray for you to be courageous and resilient again.

"We pray for you to speak out for justice, human rights and the unity of your people. We pray for you to intervene in the escalating crisis and guide your people back towards the path of righteousness again.

"It is incongruous for a symbol of righteousness to lead such a country; it is adding to our pain."