WASHINGTON — The United States on Wednesday declared the violence and atrocities against the Rohingya Muslim minority in Myanmar to be a campaign of "ethnic cleansing," and Secretary of State Rex Tillerson warned that U.S. sanctions may be forthcoming.

Tillerson blamed the Burmese military and security forces as well as local vigilantes for what he called "horrendous atrocities" that have caused more than 600,000 Rohingya to flee Myanmar's western Rakhine state for the safety of neighboring Bangladesh. But he placed most of the criticism on the government, demanding the security forces respect human rights and punish the guilty.

"Those responsible for these atrocities must be held accountable," he said in a statement, reiterating his call for an independent investigation into what has caused a refugee crisis in which Rohingya men have been executed, women raped and their babies murdered.

"The United States will also pursue accountability through U.S. law, including possible targeted sanctions," he added, suggesting sanctions might be directed against specific Burmese officials.

Many members of Congress and human rights groups had been urging Tillerson for months to adopt the "ethnic cleansing" terminology. U.N. Secretary General António Guterres designated it as such in mid-September. French President Emmanuel Macron has called it genocide. Amnesty International has called the violence in Myanmar "dehumanizing apartheid," and Human Rights Watch has termed it crimes against humanity.

State Department officials noted that ethnic cleansing is not recognized internationally as a crime and triggers no punitive measures against Myanmar, which is also known as Burma.

But it sets the stage to exert more pressure on Myanmar officials if they fail to take actions such as giving humanitarian groups and the press access to Rakhine state and guaranteeing safety to those who voluntarily return home.

Tillerson made a brief visit last week to Myanmar, where he talked with State Counselor Aung San Suu Kyi and the head of the armed forces.

The Myanmar military has denied committing atrocities during "clearance operations" to battle Muslim insurgents in the predominantly Buddhist nation. An internal investigation cleared the military of any wrongdoing.

On Aug. 25, militants belonging to the extremist Arakan Rohingya Salvation Army attacked outposts of Myanmar security forces. According to human rights groups, those forces responded with a brutal and indiscriminate crackdown on Rohingya communities, drawing in local Buddhist mobs as they went.

"No provocation can justify the horrendous atrocities that have ensued," Tillerson said in his statement.

Rohingya refugees in Bangladesh, as well as many who remain in Myanmar, have provided chilling testimony of the campaign, which they say was accompanied by widespread arson, rape and summary executions.

An exact death toll is unknown, and most aid groups and journalists have been prevented from traveling freely to the affected areas. Satellite imagery shows hundreds of Rohingya villages reduced to ashes.

Human rights groups applauded Tillerson's decision to start using the term "ethnic cleansing," but they said more action was needed.

Eric Schwartz, president of Refugees International, said the move could be used by Washington to pressure other countries to take stronger measures, including a global arms embargo and the end of military-to-military relations.

"Secretary Tillerson's statement is a necessary first step," he said. "However, until the abuses against the Rohingya people end and full access is given to the international humanitarian aid and the U.N. fact-finding mission, such pressure and requisite actions will continue to be essential."

Joanne Lin, head of advocacy and government relations for Amnesty International USA, said Tillerson's acknowledgment of ethnic cleansing sets an example for how to respond.

"The time for outrage and condemnation has passed," she said. "The international community must impose a comprehensive arms embargo and targeted financial sanctions against senior Myanmar military officials responsible for crimes against humanity."

Lin also urged the United States to introduce a U.N. Security Council resolution calling for an embargo and sanctions, and to pressure Bangladesh to loosen its registration rules so humanitarian groups can get more aid workers on the ground.

The term "ethnic cleansing" is largely descriptive and dates from the conflict in the 1990s in the former Yugoslavia. At the time, a U.N. commission defined it as "rendering an area ethnically homogeneous by using force or intimidation to remove people of given groups from the area."

The Obama administration declared the Islamic State had committed genocide against Yazidis, Christians and Shiite Muslims. In 2005, the George W. Bush administration labeled the killings in Darfur, a region of Sudan, to be genocide and tightened sanctions. But no policy was mandated by law.

"Ultimately these things come down to the politics of it," said David Bosco, an associate professor at Indiana University's School of Global and International Studies and author of a number of books on international law.

Even if the United States declared a genocide in Myanmar, Bosco added, "it's really just a question of whether that helps generate pressure for action."

Matthew Smith, co-founder of Fortify Rights, a human rights organization working in Myanmar, said Tillerson's statement was nevertheless a significant step toward holding Burmese officials accountable.

"The civilian and military authorities are aligned in their outright denials and crude whitewashing," Smith said. "Ethnic cleansing is as reprehensible as genocide and crimes against humanity."

The timing of Tillerson's statement was rife with symbolism. It coincided with the International Criminal Court's sentencing of former Bosnia Serb commander Ratko Mladic, who was convicted of genocide and crimes against humanity, to life in prison.

"The U.S. government should find more facts to declare the persecution against Rohingya is genocide," said Ro Nay San Lwin, a Rohingya blogger and activist based in Europe. "Myanmar's military commanders must be punished as Ratko Mladic was."

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The Washington Post's Adam Taylor and Brian Murphy contributed to this report.