Security has been stepped up for the Pakistan High Commissioner Shahid Malik and the Pakistani mission in New Delhi [Images] after the envoy received a  threatening letter last week.

"A request for enhancement of security was received from the Pakistan High Commission six days back after which necessary action was taken," official sources said. They, however, said the letter could be a prank played by somebody.

Pakistan High Commission sources said a three-page letter by a non-descript organisation called All India Anti-Terrorism Group asked the envoy to leave India within three days. The letter was forwarded to Ministry of External Affairs which has asked the Delhi police to investigate and take action.

The Delhi police has enhanced the security around the mission as well as Malik's residence. An additional vehicle carrying security personnel has been provided for his safety, the sources said.

So far only the US Ambassador [Images] in India has been provided an additional vehicle and security  cover amongst the envoys.

The letter referred to the alleged involvement of Pakistanis in the Mumbai [Images] terrorist attack in November that killed some 170 people. "If the threat is taken lightly, it is 200 percent sure the envoy will be killed," the letter added.