The 61-year-old Argentine leader, who was feverish when admitted on Sunday to the Otamendi Clinic in Buenos Aires, was found to be suffering from sigmoiditis, her doctors said.
Kirchner is "stable, remains in hospital under treatment with IV antibiotics, and is under observation," they added.
Due to her condition, Kirchner's meeting with her Chilean counterpart, which was set for Tuesday, has been pushed back to November, said Kirchner spokesman Alfredo Scoccimarro.
At news briefings, the government spokesman Jorge Capitanich refused to take questions on the president's health, referring reporters to her doctors' statements.
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Kirchner has had a number of health ups and downs while in office. She had resumed her normal work schedule October 21 after resting for 48 hours on doctors orders due to pharyngitis.
In July, Kirchner also had to rest for two days due to sore throat and laryngitis. Her recovery time then had to be extended to a week and she cancelled her work schedule and a trip to Paraguay.