Security agencies have pressed for questioning the estranged wife of US terror accused David Headley, as certain e-mails downloaded from his account showed her alleged complicity in the Mumbai terror attack.

The US on Saturday said it will allow Indian investigators to interrogate David Headley, who has pleaded guilty to his involvement in the Mumbai terror attacks, but made it clear that he cannot be extradited to India.

Home Minister P Chidambaram on Saturday said that India will be able to obtain access to US terror accused David Headley for questioning in a properly constituted judicial proceeding in which he is obliged to cooperate fully.

India said on Friday that the extradition of Pakistani-American David Coleman Headley to the country was still possible as there were additional charges against him, which were not part of the plea bargain he had entered into with the United States.

Pakistani-American terrorist David Headley can be interrogated by Indian investigators in the US after he confessed to plotting Mumbai attacks, even as India's efforts to extradite him hit a roadblock.