"Unvaccinated Soldiers present risk to the force and jeopardize readiness," Secretary of the Army Christine Wormuth said in a statement.

"We will begin involuntary separation proceedings for Soldiers who refuse the vaccine order and are not pending a final decision on an exemption."

More than 3,000 soldiers could be discharged, according to the statement. The army had 482,000 active duty personnel at the end of 2021.

As of January 26, six high-ranking officers -- including two battalion commanders -- had been removed from their posts for refusing to get vaccinated against Covid-19.

The army has issued written "reprimands" to 3,073 soldiers who have also refused to get vaccinated.

The US Navy announced in mid-October that personnel who declined vaccination against Covid-19 would be expelled from the force.

It has already discharged about 40 members and the Marine Corps, which is under the authority of the navy, has discharged more than 300.

The navy has been particularly sensitive to the pandemic because of the risk that a single Covid case could infect an entire ship or submarine at sea, forcing it out of action.

Around 97 percent of the approximately 1.4 million active-duty US military personnel have received at least one dose of Covid-19 vaccine, according to the Pentagon.