Secretary of State Hillary Clinton briefly left New York-Presbyterian hospital on Wednesday, only to return about 15 minutes later, the New York Daily News reported.
The State Department declined to comment on where Clinton may have gone or the status of her hospital stay. She was admitted for treatment of a blood clot in a vein behind her right ear.
Reporters witnessed Clinton leaving the hospital with her husband, former President Bill Clinton, and daughter, Chelsea, and an aide. They drove away with a security detail and a man wearing a white coat and a stethoscope.
She returned to the hospital about 15 minutes later, the Daily News reported. She had not been seen in public since Dec. 7.
A hospital spokeswoman directed all questions about Clinton, 65, to the State Department, which had no immediate comment.
Clinton's health has drawn intense media scrutiny given that she is widely considered a strong candidate for the Democratic nomination for president should she decide to run in 2016.
Clinton long ago announced her intention to step down as secretary of state. President Barack Obama, whose second term starts later this month, has nominated U.S. Senator John Kerry to replace her.
Earlier on Wednesday, a State Department spokeswoman said Clinton had been talking with her staff by telephone and receiving memos.
Clinton also spoke to two foreign officials - the U.N. envoy on Syria and the prime minister of Qatar - on Saturday, the day before the State Department disclosed the blood clot and her stay at New York-Presbyterian Hospital.
"She's been quite active on the phone with staff and taking paper, et cetera," State Department spokeswoman Victoria Nuland told the department's daily briefing.
The State Department announced on Sunday that Clinton was in a New York hospital for treatment of a blood clot that stemmed from a concussion she suffered in mid-December.
The concussion was itself the result of an earlier illness, described by the State Department as a stomach virus she had picked up during a trip to Europe that led to dehydration and a fainting spell after she returned to the United States.
In a statement released by the State Department on Monday, Clinton's doctors said they were confident she would make a full recovery and that she would be released from the hospital once the correct dosage of blood thinners had been determined.