LONDON – The Nobel laureate Desmond Tutu has sent a heartfelt letter to fellow peace prize winner Aung San Suu Kyi, condemning her for her silence over Rohingya Muslims in Burma and calling for her to intervene.

The 85-year old archbishop said the “unfolding horror” and “ethnic cleansing” in the country’s Rahkine region had forced him to speak out against the woman he admired and considered “a dearly beloved sister,” The Guardian reported.

Despite Aung San Suu Kyi defending her government’s handling of the growing crisis, Tutu urged his fellow Nobel peace prize winner to intervene.

“I am now elderly, decrepit and formally retired, but breaking my vow to remain silent on public affairs out of profound sadness,” he wrote in a letter posted on social media.

“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. You symbolised righteousness.

“Your emergence into public life allayed our concerns about violence being perpetrated against members of the Rohingya. But what some have called ‘ethnic cleansing’ and others ‘a slow genocide’ has persisted – and recently accelerated.

“It is incongruous for a symbol of righteousness to lead such a country,” said the anti-apartheid activist. “If the political price of your ascension to the highest office in Myanmar [Burma] is your silence, the price is surely too steep.”

Malala Yousafzai, the youngest-ever peace prize winner, said last Monday “the world is waiting” for Aung San Suu Kyi to act.

On Thursday, Aung San Suu Kyi made her first spoken remarks on the crisis in Rakhine since government crackdowns began last month. “It is a little unreasonable to expect us to solve the issue in 18 months,” she told the Delhi-based network Asian News International.

“The situation in Rakhine has been such since many decades. It goes back to pre-colonial times.”

More than 1,000 people may already have been killed in Burma, mostly minority Rohingya Muslims, a senior United Nations representative told AFP on Friday.

In the last two weeks alone 270,000 mostly Rohingya civilians have fled to Bangladesh, overwhelming refugee camps that were already bursting at the seams, the UN said.

Rakhine State, one of Burma’s poorest regions, is home to an estimated 125,000 stateless Rohingya Muslims, the majority of whom remain confined to temporary camps following waves of deadly violence in 2012 between Buddhists and Muslims.

Described by the UN as one of the world’s most persecuted minorities, Burma’s ethnic-Bengali Muslims, generally known as the Rohingyas, are facing a catalog of discrimination in their homeland.

They have been denied citizenship rights since an amendment to the citizenship laws in 1982 and are treated as illegal immigrants.

Burma’s government as well as the Buddhist majority refuse to recognize the term “Rohingya,” referring to them as “Bengalis.”

Construction of mosques and religious schools in the region was banned in 1962 when military rule was first established in the country.