US Secretary of State Rex Tillerson urged Myanmar's army chief on Thursday to help end the violence in Rakhine state that has forced hundreds of thousands of Rohingya Muslims to flee.

In a phone call with Min Aung Hlaing, Tillerson expressed “concern about the continuing humanitarian crisis and reported atrocities in Rakhine”, according to a statement by State Department spokeswoman Heather Nauert.

“The Secretary urged Burma's security forces to support the government in ending the violence in Rakhine state and allowing the safe return home of those displaced during this crisis, especially the large numbers of ethnic Rohingya,” she added, using Myanmar's former name.

More than 600,000 members of the minority Muslim group have fled across the border into Bangladesh in an intensifying crisis that began in late August.

Militant attacks on Myanmar security forces in Rakhine sparked a major army crackdown on the group, who are labelled illegal Bengali immigrants by most Burmese.

Tillerson, who paid a visit to Myanmar's giant neighbor India earlier this week, urged the military in his phone call to facilitate humanitarian aid for those who have been displaced.

He also told the army to “cooperate with the United Nations to ensure a thorough, independent investigation into all allegations of human rights abuses and violations and to ensure accountability,” said the statement.

Washington announced on Monday it was pushing for targeted sanctions against officers from the Myanmar army involved in violence while withdrawing invitations to senior members of the security forces to visit the US, and ending travel waivers.

The move came after Tillerson had said the US holds Myanmar's military leadership “accountable” for the refugee crisis, drawing a distinction with Aung San Suu Kyi's civilian government.

Tillerson warned last week the world won't stand and “be witness to the atrocities that have been reported,” adding that the military must be disciplined and “restrained.”

Min Aung Hlaing has consistently defended his forces against accusations of having committed atrocities.

“One-sided statements and accusations against Myanmar and security members over the terror attacks of extremist Bengalis in the west of Rakhine State are totally untrue,” he said in a post on his Facebook page on Tuesday.

Supporters say Rohingyas have been systematically deprived of basic rights over decades in majority Buddhist Myanmar.

In the latest crackdown, Myanmar's security forces have fired indiscriminately on unarmed civilians, including children, and committed widespread sexual violence, according to UN investigators.