NAYPYIDAW, Myanmar — Secretary of State Rex W. Tillerson briefly visited Myanmar on Wednesday and urged its two most influential leaders to investigate “credible reports of widespread atrocities” by the country’s security forces against Rohingya Muslims.

In a five-hour visit in Myanmar, Mr. Tillerson met with Sr. Gen. Min Aung Hlaing, the nation’s military commander, and Daw Aung San Suu Kyi, the Nobel laureate and head of the country’s civilian government. He urged both to investigate and halt the violence that has driven more than 615,000 Rohingya to flee over the border to Bangladesh since late August. Less than one-third of the 1.1 million Rohingya who lived in Myanmar last year are thought to remain in the country.

Mr. Tillerson called the situation “horrific,” and at a news conference after the meeting said that there had been “crimes against humanity.” And while he said he advised against “broad-based economic sanctions” against Myanmar, he said targeted sanctions against individuals might be called for.

Members of the mostly stateless Muslim minority are still flooding into Bangladesh from Myanmar’s Rakhine State. They bring with them accounts of villages burned to the ground, women raped and children flung into fires. The accounts have been borne out by human rights investigators and, in the case of the villages, satellite evidence.