The health of former prime minister Atal Bihari Vajpayee remained a concern with doctors putting him on "mechanical ventilation" after his respiratory infection worsened.

"He (Vajpayee) continues to have lower respiratory track infection, which has worsened since morning. He has been put on mechanical ventilation in the ICU (intensive care unit) and is being monitored by a team of doctors,"Sampath Kumar, head of the Cardiac Thoracic Vascular Sciences Department of AIIMS, said this evening.