WASHINGTON (Reuters) -The United States will test all evacuees from Afghanistan for COVID-19 and aims to set up a process for vaccinations, a senior Biden administration official said on Tuesday.

       The official said the number of Afghans coming into the United States was "fluid" due to the swiftness of the operation and could not provide a figure during a call with reporters.

       U.S. law enforcement and counterterrorism officials are carrying out "robust security processing" before evacuees are allowed to enter United States, the official said.

       President Joe Biden's administration has scrambled in recent weeks to evacuate U.S. citizens and other allies amid the chaos at Kabul airport ahead of an Aug. 31 deadline to pull out of Afghanistan.

       Afghanistan's new Taliban rulers said on Tuesday they wanted all foreign evacuations from the country completed by Aug. 31 and they would not agree to an extension.

       In the United States, flights have arrived in recent days carrying U.S. citizens and Afghans.

       After being tested for COVID-19 upon arrival, Americans can head to their homes, while others will go to a variety of U.S. military bases, where they will receive assistance in applying for work authorization, the senior official said on Tuesday.

       Those arriving Afghans will be connected with refugee resettlement organizations, the official said.

       (Reporting by Andrea Shalal and Ted Hesson in Washington; Editing by Chizu Nomiyama)