Myanmar is facing a "defining moment" and must stop the violence against its ethnic minority Rohingya population, US Secretary of State Rex Tillerson said on Thursday.
Attacks by Rohingya militants on security posts last month triggered an army operation that has killed more than 400 people, destroyed over 6800 houses and sent nearly 400,000 Rohingya Muslims fleeing to Bangladesh.
On a visit to London where he met British Prime Minister Theresa May and foreign minister, Boris Johnson, he told a news conference on Thursday: "I think it is a defining moment in many ways for this new, emerging democracy."
He said he understood that Myanmar's Aung San Suu Kyi, a Nobel prize laureate and de-facto head of the government in Myanmar, was in a power-sharing agreement with the military and the "complex situation" in which she found herself.
"I think it is important that the global community speak out in support of what we all know the expectation is for the treatment of people regardless of their ethnicity," he added. "This violence must stop, this persecution must stop."
US Senate Majority Leader Mitch McConnell earlier told the senate Suu Kyi "agreed with the need for immediate and improved access of humanitarian assistance to the region, particularly by the International Red Cross, and she conveyed that she is working toward that end".
McConnell, whose Republicans control majorities in both houses of Congress, repeated earlier criticism of a resolution introduced in the US Senate urging Suu Kyi to do more for Myanmar's ethnic minority Rohingya population, and lessening the chance that any such measure could pass.
The United Nations appealed Thursday for massive help for the nearly 400,000 who fled to Bangladesh, amid concern the number could keep rising unless Myanmar ends what critics denounce as "ethnic cleansing".
McConnell said Suu Kyi's position in the government was "exceedingly difficult" and that as a civilian, she had virtually no authority over the military.