The condition of former Indian Prime Minister Manmohan Singh, who was admitted to the All India Institute of Medical Sciences (AIIMS) in New Delhi last night, was stated to be stable today.

"He is under observation and investigation is on," according to AIIMS sources.

The 87-year-old Congress leader was admitted after he complained of uneasiness in his chestlast night, hospital sources said.

After first being taken to the hospital's cardiac care unit, or ICU for heart patients, Singh was later shifted to a private room here he will be kept under observation.

Singh developed a reaction to new medication and further investigation was on to rule out other causes of fever, the sources said.

He was the head of the Congress-led United Progressive Alliance coalition government from 2004 to 2014.