U.S. Secretary of State Hillary Clinton has returned to a New York hospital where she has been recovering for days from a blood clot in her head.

Clinton left New York Presbyterian Hospital by car Wednesday afternoon with her husband, former president Bill Clinton, their daughter Chelsea and several other people. They later returned.

There was no immediate official statement on why she left or where she went.

Earlier in the day, the State Department said Clinton was engaging by telephone with her staff in Washington who are handling U.S. foreign policy in her absence.

Secretary of State Hillary Clinton (center) is transported on the New York Presbyterian Hospital complex on Jan. 2, 2013. /AP

Clinton was admitted to the hospital Sunday for treatment of a blood clot stemming from a concussion she suffered in mid-December. While at home battling a stomach virus, Clinton fainted, fell and struck her head. The 65-year-old diplomatic chief had not been seen publicly since early last month.

Doctors found the clot in a vein that runs through the space between the brain and the skull behind her right ear. Her physicians said Monday there is no neurological damage and that they expect her to make a full recovery.

Clinton's illness has forced her to cancel travel plans and public appearances in recent weeks, including a congressional hearing on the attack on the U.S. consulate in Benghazi, Libya, on Sept. 11.