Myanmar’s de facto leader Aung San Suu Kyi has been criticized by a U.N. special rapporteur for failing to stop a brutal military crackdown on the country’s Rohingya Muslim minority which has left hundreds dead and forced more than 100,000 people from their homes.

Yanghee Lee said Nobel Peace Prize-winner Suu Kyi “needs to step in – that is what we would expect from any government, to protect everybody within their own jurisdiction.”

At least 87,000 Rohingya – a persecuted Muslim minority in predominantly Buddhist Myanmar – have been driven out by military “clearance operations” in the western state of Rakhine and pushed into neighboring Bangladesh in the past 10 days, a UNHCR spokeswoman said Monday. According to multiple reports, another 20,000 remain trapped in desperate conditions without access to food or medical supplies in Rakhine state, while at least 20 people have drowned attempting to cross a river.

The latest offensive by Myanmar’s military was launched in response to attacks by a Rohingya insurgent group, the Arakan Rohingya Salvation Army (ARSA), on August 25 that killed 12 members of security forces. Observers, including senior U.N. officials, have previously accused the military of subjecting the Rohingya to collective punishment with the goal of ethnically cleansing the Muslim minority – a charge Myanmar’s government denies.

Rakhine state is closed off to members of the media, but human rights groups report there have been mass killings in Rohingya villages carried out by military forces and local armed mobs, including a massacre in the village of Chut Pyin Wednesday, in which more than 200 people are estimated to have been killed.

Human Rights Watch has released an image which it says shows that more than 700 homes were razed in one Rohingya village, Chein Khar Li, while satellite images show many fires across Rohingya-populated areas in the north of Rakhine state.

Suu Kyi, a revered human rights icon who spent nearly 15 years under house arrest for opposing Myanmar’s then-ruling military junta, has faced mounting criticism since coming to power in 2015 for failing to halt assaults on Rohingya, who are widely viewed as one of the world’s most persecuted minorities. The Rohingya, who number about one million and live mainly in Rakhine state, are denied citizenship by Myanmar, which views them as illegal interlopers from Bangladesh. More than 100,000 have been forced to live in decrepit internally-displaced persons camps following previous bouts of communal violence, and hundreds of thousands have made perilous journeys by sea and land in their bid to flee persecution.

Critics have acknowledged Suu Kyi is in a complicated position. Security in the country remains under the control of the highly autonomous military, which ruled the country for decades, maintains a quarter of seats in parliament, and which her fledgling civilian government cannot afford to alienate.

But the catastrophe unfolding in Rakhine showed Suu Kyi needed to “step in,” said Lee. The scale of the exodus is now greater than it was during a previous military crackdown in October 2016, which sent 85,000 Rohingya across the border with accounts of murder, rape, and torture by their attackers.

Suu Kyi’s fellow Nobel Peace Laureate Malala Yousafzai joined in the criticism, issuing a statement Sunday saying she was still waiting for Suu Kyi to raise her voice. “I have repeatedly condemned this tragic and shameful treatment. I am still waiting for my fellow Nobel Laureate Aung San Suu Kyi to do the same,” she wrote.

Rather than speaking out to halt the violence, Suu Kyi disappointed many last week when her office issued a statement that accused humanitarian workers of aiding “terrorists.” The comments raised fears for the safety of aid workers in an environment where they often face suspicion and hostility from Rakhine locals and are routinely accused of a pro-Rohingya bias. Myanmar has since blocked U.N. aid agencies from delivering supplies of food, water and medicine in northern Rakhine, affecting hundreds of thousands of vulnerable displaced people.