US President Joe Biden and British Prime Minister Boris Johnson discussed Afghanistan on Tuesday and announced a virtual summit of the G7 leaders on the crisis, the White House said.

"They agreed to hold a virtual G7 leaders' meeting next week to discuss a common strategy and approach," the White House said in a statement.

This was the first phone call between Biden and a foreign leader since the startling weekend takeover by the Taliban of Kabul, prompting a panicky operation to withdraw final US and allied personnel from the city's airport.

The sudden Taliban victory has sparked fears of a large-scale humanitarian crisis both in Afghanistan and possibly involving waves of refugees seeking asylum abroad, including in western Europe.

Biden -- widely criticized for the lack of preparation in getting thousands of people airlifted to safety -- and Johnson "discussed the need for continued close coordination among allies and democratic partners on Afghanistan policy going forward," the statement said.

This includes "ways the global community can provide further humanitarian assistance and support for refugees and other vulnerable Afghans."

In London, a Downing Street spokesman said the two leaders welcomed US-British cooperation in the ongoing evacuation effort.

"They resolved to continue working closely together on this in the days and weeks ahead to allow as many people as possible to leave the country," a statement said.

"The prime minister and President Biden agreed on the need for the global community to come together to prevent a humanitarian crisis," the statement said.

It said that Johnson also "stressed the importance of not losing the gains made in Afghanistan over the last twenty years."

The G7, which Britain heads this year, comprises Britain, Canada, France, Germany, Italy, Japan and the United States.