British Prime Minister Boris Johnson

The prime minister, who spent three days in intensive care and another two weeks recovering from the disease, warned that any letup in efforts to halt it risked "a new wave of death and disease."

Foreign Secretary Dominic Raab said, "I'm confident he'll pull through." Meanwhile, the U.K. on Tuesday set a new high for COVID-19 deaths — with 786.

"Over the course of this afternoon, the condition of the prime minister has worsened and, on the advice of his medical team, he has been moved to the Intensive," U.K. officials said.

Boris Johnson is engaged to his girlfriend, Carrie Symonds. The couple is expecting their first child.

Prime Minister Boris Johnson sought an early general election in the hope of gaining ground in Parliament in support of the question that has roiled British politics since 2016: leaving the EU.