Secretary of State Hillary Rodham Clinton is under observation at a New York hospital after being treated for a blood clot stemming from the concussion she sustained earlier this month.

Clinton spokesman Philippe Reines says doctors discovered the clot Sunday while performing a follow-up exam. He would not elaborate on the location of the clot.

But he says Clinton is being treated with anti-coagulants and will remain at New York-Presbyterian Hospital through at least Tuesday.

Clinton fell and suffered a concussion in mid-December as she recovered from a stomach virus that left her severely dehydrated. She was forced to cancel a trip to North Africa and the Middle East as well as testimony before Congress about the Sept. 11 attack on the U.S. diplomatic mission in Benghazi, Libya.