A day after President Joe Biden previewed the sanctions, the Treasury Department said it was blocking any US assets and transactions with 10 current or former military officials held responsible for the February 1 coup.

The targets include General Min Aung Hlaing, the new junta chief, who already was under US sanctions over the brutal campaign against the mostly Muslim Rohingya minority.

But the sanctions also hit new individuals, including the military leaders named to a new cabinet such as Defense Minister General Mya Tun Oo.

"We are also prepared to take additional action should Burma's military not change course," Treasury Secretary Janet Yellen said, using Myanmar's former name.

"If there is more violence against peaceful protesters, the Burmese military will find that today's sanctions are just the first," she said.

The junta has voiced increasingly ominous warnings to anti-coup protesters and deployed tear gas, water cannon and rubber bullets, with isolated reports of live rounds being fired.

Secretary of State Antony Blinken renewed calls on the military regime to relinquish power, restore civilian leader Aung San Suu Kyi's elected government, release all people detained over the coup and lift communications restrictions.

"Today's action sends a clear message of support to the people of Burma in their pursuit of democracy and human rights," Blinken said.

The Treasury Department also announced sanctions on three companies dealing in the country's key gem export: Myanmar Ruby Enterprise, Myanmar Imperial Jade Co. and Cancri Co.

It said it was designating the three companies because the military controls them.

Biden in his remarks Wednesday also said the United States was cutting off the Myanmar generals' access to $1 billion in funds in the United States.