"Afghanistan is careening toward a massive, predictable, and preventable disaster," Senator Mitch McConnell said in a statement.

"The Biden administration has reduced US officials to pleading with Islamic extremists to spare our embassy as they prepare to overrun Kabul," he said.

McConnell's broadside, the strongest criticism yet by a senior official, came after the administration announced it was sending 3,000 troops to secure Kabul's international airport for a series of evacuation flights for US embassy staff and Afghans who worked for US forces.

The announcement heightened the perception that after 20 years of war the United States is abandoning the country as the Taliban insurgents claim control of city after city and increasingly threaten the Washington-backed government in Kabul.

McConnell said Biden should step up military support for the Afghan forces rather than complete the withdrawal he set for August 31.

"President Biden's strategy has turned an imperfect but stable situation into a major embarrassment and a global emergency in a matter of weeks," he said.

"If we let the Taliban dominate Afghanistan and Al-Qaeda return, it will resonate throughout the global jihadist movement."

McConnell said the decision to deploy US troops to manage the evacuation "seem(s) like preparations for the fall of Kabul," which he compared to "the humiliating fall of Saigon in 1975," when North Vietnamese troops seized control of the city two years after the US military withdrew.