U.S. President Joe Biden on Thursday ramped up the government's vaccination campaign against the spread of a contagious variant of the novel coronavirus, requiring millions of federal employees to wear masks on the job and comply with regular testing unless vaccinated.

The U.S. capital, meanwhile, said it will make indoor masks mandatory for all people over the age of 2, regardless of their vaccination status, effective Saturday morning.

U.S. President Joe Biden delivers a speech in Philadelphia on July 13, 2021. (UPI/Kyodo)

The moves came after health authorities reversed their earlier guidance and decided to ask people, even if inoculated, to wear masks indoors in parts of the country where the number of infections is substantially higher, citing concerns over the highly transmissible Delta variant.

As additional efforts to slow the spread of the Delta variant, which was first detected in India, Biden said every federal government employee and onsite contractor will be asked to attest to their vaccination status.

Anyone who does not attest to being fully vaccinated will be required to wear a mask during work no matter their geographic location, physically distance from all other employees and visitors and undergo a weekly or twice weekly screening testing, he said.

According to the White House, the federal government employs more than 4 million Americans, including over 2 million in the federal civilian workforce, at home and abroad.

Biden also said he is directing the Defense Department to look into adding COVID-19 vaccination to the list of required vaccinations for members of the military, while calling on states and local governments to do more to incentivize vaccination, including offering $100 to those who get vaccinated.

With rules on face-covering often being a subject of dispute between Democrats and Republicans, the Democrat president insisted that a mask is "not a political statement." Some polls have showed that Republicans tend to be more hesitant about getting vaccines.

"Look, this is not about red states and blue states. It's literally about life and death. That's what it's about," Biden said, referring to the symbol colors of the two parties.