By Idrees Ali and Jonathan Landay

WASHINGTON (Reuters) -The United States will reduce staff at the embassy in Kabul to a “core diplomatic presence” and send about 3,000 troops temporarily to the airport to assist as the Taliban made rapid gains in Afghanistan, officials said on Thursday.

The news of the embassy drawdown, first reported by Reuters, is one of the most significant signs of concern in President Joe Biden’s administration about the security situation and the failure of the Afghan government to protect key cities.

“We’ve been evaluating the security situation every day to determine how best to keep those serving at the embassy safe,” State Department spokesman Ned Price told reporters.

“Accordingly we are further reducing our civilian footprints in Kabul in light of the evolving security situation,” Price said.

“We expect to draw down to a core diplomatic presence in Afghanistan in the coming weeks,” he said, adding that the embassy was not closed.

The Pentagon said that it would send about 3,000 additional U.S. troops temporarily to Afghanistan to help secure the drawdown of personnel.

Pentagon spokesman John Kirby said the first deployment would occur in the next 24 and 48 hours to the airport in Kabul.

About 3,500 additional U.S. troops would be sent to the region to be on standby if the situation worsened, as well as 1,000 personnel to help process Afghans going through a special immigration process.

It is common for the U.S. military to send in large number of troops to evacuate personnel in combat zones.

There are thought to be about 1,400 staff remaining at the U.S. Embassy in Kabul. Officials, speaking on the condition of anonymity, said the reduction in staff was “significant.”

The military mission in Afghanistan is set to end on Aug. 31, and roughly 650 troops remain in the country to protect the airport and embassy.

A source familiar with the situation said that the United Kingdom was expected to make a similar announcement about relocating staff.

Afghanistan’s third-largest city, Herat, was on the verge of falling to the Taliban on Thursday amid heavy fighting, as the militant group also established a bridgehead within 150 km (95 miles) of Kabul.

The spiraling violence and the militants’ swift advances prompted the United States and Germany to urge their citizens to leave the country immediately.

A U.S intelligence assessment this week said the Taliban could isolate Kabul within 30 days and take it over in 90.

(Reporting by Idrees Ali and Jonathan Landay. Additional reporting by Patricia Zengerle, Humeyra Pamuk, Arshad Mohammed, Simon Lewis; Editing by Cynthia Osterman and Rosalba O’Brien)