The United States intensified its sanctions against Myanmar on Friday, blacklisting four commanders and two units of security forces for their alleged role in violent campaigns against Rohingya Muslims and other ethnic minorities.

Myanmar security forces have engaged in ethnic cleansing, massacres, sexual assault, extrajudicial killings and other human rights abuses, said Sigal Mandelker, Treasury Department undersecretary for terrorism and financial intelligence. "Treasury is sanctioning units and leaders overseeing this horrific behavior as part of a broader U.S. government strategy to hold accountable those responsible for such wide-scale human suffering."

The Trump administration earlier imposed sanctions on the chief of Myanmar's western military command, but has faced pressure from human rights groups and lawmakers to impose more sanctions on those involved in a crackdown that began in August 2017 in western Rakhine State where a brutal military operation in response to attacks on security forces sent 700,000 Rohingya fleeing to neighboring Bangladesh.

The Rohingya have long faced severe discrimination in the majority Buddhist nation and were the target of violence in 2012 that killed hundreds and drove more than 140,000 people — predominantly Rohingya — from their homes to camps for the internally displaced.

The government refuses to recognize the Rohingya as a legitimate native ethnic minority and most Rohingya are denied citizenship and other rights. Myanmar, however, has staunchly denied that its security forces have targeted civilians in so-called clearance operations in Rakhine State on Myanmar's west coast.

Friday's action sanctions four commanders with the Myanmar military and border guard police plus two military units for their alleged involvement in ethnic cleansing in Rakhine and other human rights abuses in Myanmar's northern Kachin and Shan states, the scene of separate, ethnic armed insurgencies against the central government. Those sanctioned are: military commanders Aung Kyaw Zaw, Khin Maung Soe, Khin Hlaing and Thura San Lwin; and members of the 33rd and 99th light infantry divisions.

The sanctions block any property they own within U.S. jurisdiction and prohibit U.S. citizens from engaging in transactions with them. The U.S. already maintains restrictions on visas, arms sales and assistance to Myanmar's military.

In a statement, Myanmar's embassy in Washington said: "Security forces have been instructed to adhere strictly to the code of conduct in carrying out security operations, to exercise all due restraint, and to take full measures to avoid collateral damage and the harming of innocent civilians. No one is above the law in present Myanmar and those who breach the law will be brought to justice."

The crackdown on the Rohingya has cast a shadow over Myanmar's transition to democracy after decades of direct military rule and has set back a rapprochement with Washington initiated by the Obama administration. Myanmar's civilian leader, Nobel peace laureate Aung San Suu Kyi, has little control over security operations but has faced stark international criticism for failing to protect the Rohingya.

On Friday, 17 U.S. senators appealed to Secretary of State Mike Pompeo to make public a State Department report detailing atrocities conducted against the Rohingya and submit the report to the department's Office of the Legal Adviser for a determination of whether crimes against humanity and genocide were perpetrated by the security forces in Myanmar, also known as Burma.

The U.S. declared in November that there's been "ethnic cleansing" against the Rohingya but that isn't recognized as an independent crime under international law, whereas crimes against humanity and genocide are.

"The Burmese military has murdered thousands of Rohingya; committed widespread rape and sexual violence; razed hundreds of villages; thrown babies into fires; and employed mass graves in an attempt to conceal their terrible crimes," the letter said.

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Associated Press writer Matthew Pennington contributed to this report.