He said the Rohingya had suffered “horrendous atrocities” and as a result the US was considering targeted sanctions against those responsible.
Mr Tillerson’s comments come days before a visit to Myanmar by the Pope.
The Rohingya are a stateless minority who have long experienced persecution in Myanmar, also known as Burma. More than 600,000 have fled to neighbouring Bangladesh since violence erupted in Rakhine state late in August.
“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,” Mr Tillerson said in a statement.
“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.
He said the US wanted an independent investigation into events in Rakhine state and targeted sanctions could follow.
“Those responsible for these atrocities must be held accountable,” he added.
Tillerson’s comments reflect a hardening US stance on Myanmar in recent days. On a one-day visit to the country last week he said Washington was “deeply concerned” by reports of widespread atrocities.
He urged the government and security forces to respect the human rights of all those within its borders. (Courtesy BBC)