Official sources told IANS Monday that intelligence agencies had advised the government to enhance the security of the two VIPs, after they intercepted Maoist messages "planning revenge" for the killing of Communist Party of India-Maoist leader and spokesperson Cherkuri Rajkumar alias Azad in Andhra Pradesh recently.
Earlier, Chidambaram and Pillai were accompanied by security personnel carrying small arms. The number of security officials accompanying the two have also been enhanced.
Official sources said all offices and buildings to be visited by Chidambaram and Pillai would be subjected to stricter searches.
Azad, a key member of the central committee of the outlawed CPI-Maoists, was killed in an gunfight with Andhra Pradesh Police in the jungles bordering Maharashtra. However, the Maoists alleged that it was a staged gunfight.
Civil rights activists had demanded a judicial probe into the killing of Azad.
Government sources said the intelligence reports spoke of "doing something spectacular" against the "rulers in Delhi" to avenge the killing of Azad, and therefore the security cover for Chidambaram and Pillai have been upgraded.