Biden spoke hours after the blasts killed at least a dozen American troops and scores of civilians, the worst day of casualties for U.S. forces there in a decade
After Johnson chaired an emergency response meeting on the situation in Afghanistan, he said Britain's airlift would continue "going up until the last moment".
Pentagon spokesperson John Kirby said the head of U.S. forces in Afghanistan still had that authority, even as the U.S. closes in on a military withdrawal from Afghanistan.
Biden has asked Congress to approve $3.3 billion in security assistance for Afghanistan next year and is sending 3 million doses of vaccines there to help it battle COVID-19.
The U.S. officials did not disclose where the Afghans would be sent or how many would be evacuated but said the group consisted entirely of Afghans who have already started the visa process.