XIII Metropolitan Magistrate S Sivasubramanyam extended the remand when 37-year-old Hussain, arrested here on April 29 by Tamil Nadu Q Branch police, when he was produced before him.
He also issued a non-bailable warrant against one Mohammed Hussain, an accomplice of Zahir Hussain, a Sri Lankan national.
The Metropolitan Magistrate turned down a plea of Hussain a suspected ISI agent, to talk with his pregnant wife in Sri Lanka.
Zahir Hussain, suspected to be acting on the instructions of ISI men in Colombo, had planned to carry out terror attacks on foreign missions in South India.