Secretary of State Rex Tillerson shakes hands with Burmese leader Aung San Suu Kyi. (Aung Shine Oo/AP)

SECRETARY OF STATE Rex Tillerson too often has shown a disregard for human rights issues, especially in his public diplomacy. So his news conference in Burma on Wednesday was a welcome departure. Standing next to the country's civilian leader, Aung San Suu Kyi, Mr. Tillerson spoke forcefully about "credible reports of widespread atrocities committed by [Burma's] security forces" against the Rohingya ethnic minority. He said the campaign, which has driven more than 600,000 people across the border to Bangladesh, "has a number of characteristics of certainly crimes against humanity."

Mr. Tillerson repeatedly called for a "credible" and "independent" investigation, said that those guilty of abuses should be held accountable, and indicated that U.S. sanctions against involved individuals would be appropriate. He also called on the government to allow the voluntary return of the Rohingya and provide them with "a transparent and fully voluntary path to citizenship," which most lack. "Myanmar's response to this crisis," he said, using the name for the country favored by the regime, "is critical to determining the success of its transition to a more democratic society."

Mr. Tillerson's connection of "the humanitarian scandal" of the Rohingya to Burma's democratic transition was particularly significant. Aung San Suu Kyi, who lacks authority over the country's military, has attempted to sidestep the crisis, offering bland statements about the need for "harmony" and establishing commissions with vague missions. Her aides say her priority is consolidating democracy by gaining the military's support for changes to the constitution, which now gives the generals an overwhelming role. Given the scale of the offenses, which U.N. officials have labeled "ethnic cleansing" and members of Congress have called "genocide," that's a blinkered view. As Mr. Tillerson said, "the key test of a democracy is how it treats its most vulnerable and marginalized populations."

Mr. Tillerson appeared intent on offering Aung San Suu Kyi another chance to do the right thing, saying the independent investigation he called for should be led by "Myanmar's civilian government." That drew scorn from international human rights advocates, who said Mr. Tillerson should have supported an international fact-finding mission sponsored by the United Nations and demanded that the government reverse its refusal to allow U.N. observers into Rakhine state, where the military has torched scores of Rohingya villages and allegedly carried out systematic rapes and murders.

Mr. Tillerson is understandably seeking to preserve the U.S. relationship with Aung San Suu Kyi, a Nobel Peace Prize winner who courageously opposed military rule for decades. The alternative could be a regime that would reverse the democratic opening and ally itself with China. But critics' skepticism is well founded: It is highly doubtful that Aung San Suu Kyi's government will or can carry out the credible investigation the United States, along with much of the rest of the world, asks for. In the absence of prompt action to create conditions for the voluntary return of the Rohingya and for steps to identify and hold accountable those responsible for atrocities, the Trump administration should proceed with sanctions against senior military leaders, support an international embargo on arms sales and explicitly back the U.N. investigation.