As part of his plea deal, Headley will not face execution if he continues to cooperate with U.S. prosecutors' terrorism investigation.
Indian Home Minister Palaniappan Chidambaram said India had yet to receive permission from U.S. authorities to speak with Headley or his wife.
"We will continue to press our request for access to interrogate him," Chidambaram told reporters.
Chidambaram said he also planned to continue to push a request to extradite Headley to face charges in India but had little hope of success because the plea agreement expressly forbade his extradition to India, Denmark and Pakistan.
The 60-hour Mumbai siege left 166 people dead. Nine attackers – all of whom were based in Pakistan – were killed, while a tenth suspect is on trial in Mumbai.