Thousands of armed security personnel on Wednesday kept a hawk-eyed vigil over the capital to pre-empt any possible terror strike on Independence Day.
An elaborate ground-to-air security apparatus was put in place in the city, especially near Red Fort where Prime Minister Manmohan Singh unfurled the tri-colour and addressed the nation for the ninth consecutive time.
Security agencies left no stone unturned to ensure an incident-free Independence Day celebrations even though there was no specific intelligence input about a possible terror strike.
The Union home ministry has already issued a country-wide alert asking states to tighten security at sensitive locations and installations to thwart any attempt of terror strike.
A senior police official said elaborate security arrangements have been made and personnel from Delhi Police and paramilitary were deployed.
Around 50 CCTVs have been installed in and around the Red Fort to ensure peaceful celebrations while sharpshooters of the NSG were deployed on the high-rises near the 17th century Mughal monument.
Besides the Red Fort, the official said, intense vigil was being maintained on key installations like Parliament complex, international airport, railway stations, inter-state bus terminals and Metro stations.
"The localities around the Red Fort have been sanitised before the event and informers were deployed to keep a check on any movement of anti-national elements," the official said.
Specialised units like Quick Reaction Teams, SWAT and Vajra were also deployed.
A no-fly zone was put in place around the Red Fort for the nearly 90-minute function.
Besides patrolling of the skies by helicopters, an air defence mechanism was also kept in readiness around the venue to thwart any terror attacks.
Delhi Police carried out intensive checks at all the border points.