Vajpayee has knee surgery

Mr Vajpayee at a religious festival: Health concerns have grown

India's Prime Minister, Atal Behari Vajpayee, has undergone an operation to replace his left knee joint.

The New York-based surgeon who carried out the procedure, Chittaranjan Ranawat, told journalists that the operation had gone well.

Mr Vajpayee, 75, is expected to recuperate for at least the next few days in bed in the exclusive Breach Candy hospital in Bombay, where the operation was carried out.

As the surgery went ahead, hundreds of supporters of his party, the BJP, offered prayers at nearby temples.

Physiotherapy

Dr Ranawat said the prime minister had been administered local anaesthesia and was conscious throughout the operation.

Mr Vajpayee is expected to begin physiotherapy on Tuesday evening and will be made to walk a few steps the next day.

His stay at hospital will last anything between five and 15 days.

Mr Vajpayee has looked increasingly frail in public recently, and clearly has difficulty walking and standing.

Last month, poor health forced him to cut short a landmark visit to the United States.

Officials said osteoarthritis was the cause of the problem.

Mr Vajpayee has not named a deputy to cover for him while he is hospital.

Staying at the helm

Although it is expected to be about two weeks before he is walking again, he says he will continue in office throughout.

In the meantime, the prime minister's office is being run from the hospital.

The BBC's Jill McGivering in Delhi says the operation has raised questions about who could replace Mr Vajpayee if that became necessary.

Many analysts say it is Mr Vajpayee's moderate and diplomatic style which is making it possible for the present multi-party coalition to survive intact.

Finding a replacement capable of sustaining that balancing act might not be easy.

Officials deny reports that Mr Vajpayee has suffered from prostate cancer, but his physical difficulties in recent weeks have fuelled speculation about his general health.