US Secretary of State Rex Tillerson called Myanmar leader Aung Sang Suu Kyi on Tuesday to urge her government to address "deeply troubling allegations of human rights abuses and violations."
More than 400,000 members of Myanmar's Rohingya minority have fled fighting in Rakhine state.
The United States has previously expressed concern about the crisis, but has been cautious about blaming Nobel Peace laureate Suu Kyi directly for the alleged abuses, and Tuesday's call was Tillerson's first.
"The secretary welcomed the Burmese government's commitment to end the violence in Rakhine State and to allow those displaced by the violence to return home," State Department spokeswoman Heather Nauert said.
"He also urged the Burmese government and military to facilitate humanitarian aid for displaced people in the affected areas, and to address deeply troubling allegations of human rights abuses and violations."
Earlier in the day, Suu Kyi -- in an address timed to pre-empt censure at the UN General Assembly in New York -- pledged to hold human rights violators to account, but refused to blame the military for the attacks.
She called for patience and understanding of the crisis, which has driven some 421,000 Muslim Rohingya out of her mainly Buddhist country, but failed to quell mounting international outrage.