Secretary of State Rex Tillerson on Wednesday called the Myanmar military operation against the Rohingya population "ethnic cleansing" and said the United States would consider targeted sanctions against those responsible.
Referring to "horrendous atrocities" that have occurred, Mr Tillerson said in a statement on Wednesday: "After a careful and thorough analysis of available facts, it is clear that the situation in northern Rakhine state constitutes ethnic cleansing against the Rohingya."
While a top UN official has described the military actions as a textbook case of "ethnic cleansing", Mr Tillerson left Myanmar after a visit last week without using the label.
His statement made clear the US stance has shifted.
"These abuses by some among the Burmese military, security forces, and local vigilantes have caused tremendous suffering and forced hundreds of thousands of men, women, and children to flee their homes in Burma to seek refuge in Bangladesh," he said.
The United States supports an independent investigation into what happened in Rahkine state and will pursue action through US law, including possible targeted sanctions, he said.
"Those responsible for these atrocities must be held accountable," Mr Tillerson said.
In early November, US lawmakers proposed targeted sanctions and travel restrictions on military officials in Myanmar, also known as Burma.
Human rights monitors have accused Myanmar's military of atrocities, including mass rape, against the stateless Rohingya during so-called clearance operations following insurgent attacks on 30 police posts and an army base.
Myanmar's two-year-old government, led by Nobel laureate Aung San Suu Kyi, has faced heavy international criticism for its response to the crisis, though it has no control over the generals it has to share power with in the country's transition to civilian power after decades of military rule.