The United States on Tuesday stiffened sanctions against Myanmar's army chief over the mass killings of Rohingya, as his country defended itself against genocide charges before the top UN court.

The United States in July banned military chief Min Aung Hlaing from visiting, but Tuesday's move goes further by freezing any US assets and criminalizing financial transactions with him by anyone in the United States.

The Treasury Department imposed the same sanctions on three other senior Myanmar commanders, as well as 14 individuals from other countries, to observe International Human Rights Day.

"The United States will not tolerate torture, kidnapping, sexual violence, murder or brutality against innocent civilians," Treasury Secretary Steven Mnuchin said in a statement.

"America is the world leader in combatting human rights abuse and we will hold perpetrators and enablers accountable wherever they operate."

Myanmar's military is accused of leading a brutal campaign in 2017 in Rakhine state against the Rohingya, a mostly Muslim minority whom the Buddhist-dominated nation does not consider citizens.

Around 740,000 Rohingya fled to neighbouring Bangladesh after a crackdown by the Myanmar military in 2017 that UN investigators have already described as genocide.

© AFP