The 76-year-old Prime Minister "continues to make excellent progress in his recovery following the heart surgery. He sat up this morning and had semi-solid food," PM's Media Adviser Deepak Sandhu said.

Noting that several of his 'invasive monitoring lines' have been removed, she said Singh was undergoing physiotherapy to enable early mobilisation.

"The Prime Minister was conversing with family members and the doctors attending to him," Sandhu said, adding that he was eager to resume work as soon as possible.

Dr Vijay D'Silva, who is taking care of Singh at the ICU at the All India Institute of Medical Sciences since the operation on Saturday, said the Prime Minister was "recovering well and his vital parameters are stable."

On Prime Minister's diet, D'Silva said Singh had taken coconut water and porridge this morning.

Sandhu said the Prime Minister is "deeply touched" by countless 'get well soon' messages sent to him from across the country.

"The Prime Minister is specially overwhelmed by the abundance of good wishes that have come from children, many of whom have prayed for his quick recuperation," she said.

"Singh is thankful to the people whose love for him has always been a source of great strength to him and particularly as he recovers from the surgery," Sandhu said, adding that the Prime Minister's family also joined him in expressing heartfelt gratitude to the people for their support during this period.

The Prime Minister has also received messages wishing him speedy recovery from several world leaders, she added.

Five grafts were carried out to overcome the blockages to Singh's heart at AIIMS on Saturday.

A team of doctors from the Asian Heart Institute, Mumbai, had performed the over 11-hour-long operation on the Prime Minister. They were helped by three AIIMS doctors and several support staff.

Dr K S Reddy, personal physician to the Prime Minister, had yesterday said that in four weeks, Singh can do virtually all work and could be fit even for a public meeting.

The date of discharge has not been finalised, but considering his progress, the doctors do not think that Singh would have to remain there for long, he had said.

Reddy had said that the Prime Minister would remain in the hospital at least for another five to six days.

Security strengthened at AIIMS as fog envelops the premises

Security at the All India Institute of Medical Sciences, where Prime Minister Manmohan Singh is recuperating after a re-do bypass surgery, has been strengthened after thick blanket of fog enveloped the hospital premises early this morning.

Delhi Police personnel, who were till now deployed on the route towards the Cardio Vascular Thoracic Surgery (CVTS) unit where the PM has been recuperating, fanned to different locations of the hospital premises as the fog descended at around 5 a.m.

"Because of the fog, the personnel have been asked to cover other areas of the AIIMS premises -- like the Out Patient Department (OPD), Emergency centre, Paediatrics among others," a senior police official, present at the AIIMS said.

The arrangement is just to make sure that the area is secure and there will not be any constant deployment, the official said.

Fog descended the hospital premises at round five this morning reducing the visibility to only a few metres.

The security near the CVTS unit has also been beefed up with deployment of more Special Protection Group (SPG) men and Delhi Police commandos at the exit of the unit.

The police personnel have been posted at different vantage point on the route the CVTS. About 20-25 policemen were brought in at around 12.30 am to be deployed on the AIIMS premises.

The AIIMS security guards have removed the pavement dwellers from the premises near the OPD area. Only patients and their attendants, who have their medical cards with them, were allowed to enter the respective departments.

"This has been done keeping in mind the security concerns, as the Prime Minister is admitted here and also it is a Republic Day today," a security officer at the AIIMS said on the condition of anonymity as he was not authorised to speak to media.

he AIIMS spokesperson was not available for the comment.