NAYPYITAW -- U.S. Secretary of State Rex Tillerson was in Myanmar on Wednesday to meet with leader Aung San Suu Kyi amid a crisis in the country's west that has seen hundreds of thousands of Muslim Rohingya flee to Bangladesh.

Suu Kyi's office confirmed that Tillerson would meet with her during his one-day visit, which comes as a new report said there was "mounting evidence" of genocide against the Rohingya in Myanmar.

Tillerson was expected to hold talks about the situation in northern Rakhine state, where a government security operation has caused more than 600,000 Rohingya to flee to neighboring Bangladesh.

He was also to meet with Myanmar's powerful military chief, Min Aung Hlaing, who is in charge of operations in Rakhine.

A senior U.S. State Department official said Tuesday that Tillerson would use the visit to "express concerns over the displacement and violence and insecurity affecting Rohingya populations and other local populations and discuss ways to help Burma stakeholders implement commitments aimed at ending the crisis and charting productive ways forward."

Get Breaking News Delivered to Your Inbox

Myanmar was formerly known as Burma.

Tillerson's visit comes as a new report issued by the United States Holocaust Memorial Museum and the advocacy group Fortify Rights found there is "mounting evidence" of genocide against the Rohinyga in Myanmar. It accused security forces and civilians of mass killings - including burning victims as young as infants alive - rape and other abuses, and called on the international community to take action.

"These crimes thrive on impunity and inaction," said Matthew Smith, the head of Fortify Rights. "Condemnations aren't enough. Without urgent international action towards accountability, more mass killings are likely."

Speaking Wednesday after his arrival, Tillerson described the images of Rohingya Muslims fleeing Rakhine as "just horrific," according to the Reuters news agency. He said he was "encouraged" by the ongoing discussion between Myanmar and Bangladesh, and he pledged $47 million in new aid from the U.S. to help the refugees.

Myanmar's military has denied the accusations, most recently with a statement Monday. The military said it had interviewed thousands of people during a monthlong investigation into the conduct of troops in Rakhine after Rohingya insurgents launched a series of deadly attacks there on Aug. 25.

While the report acknowledged that battles against militants from the Arakan Rohingya Salvation Army had left 376 "terrorists" dead, it also claimed security forces had "never shot at the innocent Bengalis" and "there was no death of innocent people."

Myanmar's government and most of the Buddhist majority say the members of the Muslim minority are "Bengalis" who migrated illegally from Bangladesh and do not acknowledge the Rohingya as a local ethnic group even though they have lived in Myanmar for generations.