New Delhi - Former Indian prime minister Atal Behari Vajpayee was in a serious condition Saturday as he fought a respiratory infection, officials at the Delhi hospital treating him said.

"He is in a serious but stable condition and continues to be on mechanical ventilation following lower respiratory tract infection," the All India Institute of Medical Sciences
(AIIMS) medical superintendent DK Sharma said.

Vajpayee, 85, was admitted to the intensive care unit of hospital on Tuesday night, after he complained of difficulty in breathing Tuesday night.

The only person to have been served three times as prime minister of India, Vajpayee is a leader of the Bharatiya Janata Party (BJP).

The coalition led by his party lost to a Congress Party-led alliance in the 2004 general election and is now the country's main opposition.

Vajpayee has been suffering from ill health for the past three years and retired from active politics.

Congress Party president Sonia Gandhi and Parliament Speaker Somnath Chatterjee were among leaders who visited Vajpayee in hospital Saturday.

"His condition is being constantly monitored and his health parameters like blood pressure and kidney and liver functions are normal," Sharma said. (dpa)