Clinton's doctors discovered the clot Sunday while performing a follow-up exam, her spokesman, Philippe Reines, said. He would not elaborate on the location of the clot but said Clinton is being treated with anti-coagulants and would remain at New York-Presbyterian Hospital for at least the next 48 hours so doctors can monitor the medication.

"Her doctors will continue to assess her condition, including other issues associated with her concussion," Reines said in a statement. "They will determine if any further action is required."

Clinton, 65, fell and suffered a concussion while at home alone in mid-December as she recovered from a stomach virus that left her severely dehydrated. The concussion was diagnosed Dec. 13 and Clinton was forced to cancel a trip to North Africa and the Middle East that had been planned for the next week.

Clinton was also forced to cancel Dec. 20 testimony before Congress about a scathing report on the Sept. 11 attack on the U.S. diplomatic mission in Benghazi, Libya, that killed Ambassador Chris Stevens and three other Americans. The report found that serious failures of leadership and management in two State Department bureaus were to blame for insufficient security at the facility. Clinton took responsibility for the incident before the report was released, but she was not blamed.

Some conservative commentators suggested Clinton was faking the seriousness of her illness and concussion to avoid testifying, although State Department officials vehemently denied that was the case.

Lawmakers at the hearings -- including Democratic Sen. John Kerry, the Senate Foreign Relations Committee chairman who has been nominated by President Barack Obama to succeed Clinton -- offered her their best wishes.

The former first lady and senator, who had always planned to step down as America's top diplomat in January, is known for her grueling travel schedule. She is the most traveled secretary of state in history, having visited 112 countries while in the job.

<관련 한글 기사>

힐러리, 뇌진탕 후유증으로 입원

최근 뇌진탕 증세로 자택에서 요양중이던 힐러리 클린턴 미국 국무장관이 혈전이 발견돼 일요일 뉴욕장로병원에 입원했다.

필립 레인스 국무장관 대변인은 이날 "힐러리 장관이 뇌진탕 후유증으로 혈액응고 등의 문제를 겪고 있다"며 "이를 위해 병원에 입원해 치료를 받고 있다"고 말했다. 그녀는 이틀간 병원에 머물며 치료를 이어갈 예정이다.

클린턴 장관(65)은 이달 초 유럽 순방 도중 바이러스성 위장병에 걸려 모든 일정을 취소하고 홀로 자택에서 요양 중이었다. 지난 13일에는 위장병에 따른 탈수증세로 의식을 잃고 넘어져 뇌진탕 진받을 받았다. 이로 인해 20일로 예정돼있던 리비아 벵가지 주재 미국 영사관 피습사건 청문회에 불참하기도 했다.