WASHINGTON (Reuters) - The State Department is considering formally declaring the crackdown on Myanmar’s Rohingya Muslims to be ethnic cleansing, U.S. officials said on Tuesday, as lawmakers called for sanctions against the Southeast Asian country’s military.

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Pressure has mounted for a tougher U.S. response to the Rohingya crisis ahead of President Donald Trump’s maiden visit to Asia next month when he will attend a summit of Southeast Asian countries, including Myanmar, in Manila.

U.S. officials are preparing a recommendation for Secretary of State Rex Tillerson that would define the military-led campaign against the Rohingya as ethnic cleansing, which could spur new sanctions, the U.S. government sources said.

The proposal - part of an overall review of Myanmar policy - could be sent to Tillerson as early as this week, and he would then decide whether to adopt it, according to the officials, who spoke on condition of anonymity.

More than 600,000 Rohingya Muslims have fled Rakhine state in Buddhist-majority Myanmar, mostly to neighboring Bangladesh, since security forces responded to Rohingya militants’ attacks on Aug. 25 by launching a crackdown. The United Nations has already denounced it as a classic example of ethnic cleansing.

Three U.S. officials testifying at a Senate hearing on Tuesday declined to say whether the treatment of the Rohingya was ethnic cleansing, but listed new measures including targeted sanctions that Washington is considering.

Those steps, however, stopped short of the most drastic tools at Washington’s disposal such as reimposing broader economic sanctions suspended under the Obama administration.

“I’m not in a position ... to characterize it today, but to me this very closely resembles some of the worst kind of atrocities that I’ve seen during a long career,” Deputy Assistant Secretary of State Mark Storella said when pressed to say whether he viewed the situation as ethnic cleansing.

Senator Ben Cardin, the ranking Democrat on the Foreign Affairs Committee, said he considered the treatment of the Rohingya “genocide” and is working on bipartisan legislation that could spell out whether additional sanctions are needed.

Myanmar, also known as Burma, insists that action was needed to combat “terrorists.”

The recommendation to Tillerson - first reported by the Associated Press - is not expected to include a determination on whether “crimes against humanity” have been committed, as this would require further legal deliberations, one U.S. official said.

The State Department did not immediately respond to a request for comment.

Some U.S. lawmakers criticized Aung San Suu Kyi, head of Myanmar’s civilian-led government and a Nobel peace laureate once hugely popular in Washington, for failing to do more.

Senator Bob Corker, Republican chairman of the committee, chided Suu Kyi for what he called “dismissiveness” toward the plight of the Rohingya and said it might be time for a “policy adjustment” toward Myanmar.

At the hearing, Patrick Murphy, Deputy Assistant Secretary of State for East Asian And Pacific Affairs, said additional sanctions were being considered, but cautioned that doing so could lessen Washington’s ability to influence Myanmar.