Already on high alert following last week's bomb blast outside the Delhi High Court, security has been further beefed up in the national capital following an email which threatened of a possible blast in a shopping mall this week.
Around 20,000 police personnel have been deployed to carry out extensive searches on vehicles, suspicious people and premises across the capital, a senior police official said.
The official said all precautionary measures are being taken in view of the threat perception ahead of the third anniversary of September 13, 2008 blasts that claimed over 20 lives.
Police have already strengthened security at shopping malls by deploying more personnel and conducting extensive searches.
The police official said the force is on high alert and they had intensified patrolling and checking across the city, including shopping malls, markets and other crowded places.
He said more people are being deployed and shopping mall operators have been asked to step up their security system. They are also being periodically briefed about the security arrangements they should make, he said.
Police have also intensified checking at border points of the national capital.