Referring to "horrendous atrocities" that have occurred, Tillerson said in a statement, "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".
Although a top United Nations official in September described the military actions as a textbook case of "ethnic cleansing", Tillerson left Myanmar, also known as Burma, after a visit last week without using the label.
Hundreds of thousands of Rohingya have fled Rakhine State in recent months amid the violence.
While the army insists it has only targeted Rohingya rebels, refugees massing in Bangladeshi camps have given chilling and consistent accounts of widespread murder, rape and arson at the hands of security forces and Buddhist mobs.
The army and administration of de facto civilian leader Aung San Suu Kyi - a Nobel peace laureate - have dismissed reports of atrocities and refused to grant entry to United Nations investigators tasked with probing allegations of ethnic cleansing.
In Washington, the U.S. State Department is considering whether to officially designate the conflict as ethnic cleansing.
British Prime Minister Theresa May's spokesman said on November 13 the actions of the military in Rakhine State "looks like ethnic cleansing", adding it was a "major humanitarian crisis".
Meanwhile, the military's True News Investigation Team last week announced an internal investigation had exonerated Myanmar's armed forces of any abuses during the security crackdown that followed the attacks.
Various rights groups said there was mounting evidence that Myanmar army was conducting in a genocide against the Muslim minority.
Desserts Needed for Salvation Army's Thanksgiving Lunch
The 33rd Annual free Thanksgiving Meal for the community will take place on Thursday at its new Hospitality House located 1002 N. Green has been cooking turkeys for the Salvation Army's Thanksgiving for the last 14 years, both smoking and frying the turkeys.