Security has been beefed up near the residence of All India Anna Dravida Munnetra Kazhagam supremo Jayalalithaa after an anonymous letter threatening to kill the former chief minister was received, police said on Monday.
The letter, received at the office of Jaya TV on Sunday, threatened to kill Jayalalithaa using bombs.
It also asked the channel to 'stop its criticism against Chief Minister M Karunanidhi'.
After the letter was received, an official of the channel lodged a complaint with Chennai Police Commissioner Letika Saran on Sunday night.
Saran said police was taking all steps to avoid any untoward incident.
"Bomb disposal squads will be in place at the Jaya TV office and patrolling and other security measures near the residence of Jayalalithaa have been intensified," she told PTI.
The origin of the letter will be traced soon and a case has been registered with the Central Crime Branch of the Chennai Police, she said.