Austin -- whose return comes a day after a deadly attack on American troops in the Middle East -- was due to meet NATO Secretary General Jens Stoltenberg for bilateral talks on Monday.

Austin "returned to work at the Pentagon today. The secretary has been conducting his duties from home since his release from Walter Reed National Military Medical Center on January 15, 2024," the Defense Department said in a statement.

The 70-year-old career soldier initially underwent minor surgery to treat prostate cancer on December 22, returning home the following day, but was readmitted due to complications including nausea and severe pain on January 1.

The White House was not informed about Austin's hospitalization until January 4, while Congress was not told until the following day, and Biden did not learn of the cancer diagnosis until January 9.

Austin made his first public appearance since his hospitalization last week, speaking via videolink from his residence at the opening of a meeting on aid for Ukraine.

After he went to Walter Reed for a follow-up appointment Friday, two doctors said Austin is likely to make a "full recovery" and that his prognosis is "excellent."

Republican lawmakers have called for Austin to be sacked, but US President Joe Biden, while lamenting the Pentagon chief's lapse in judgment, has said he remains confident in his defense secretary.