New Delhi, March 20 (IANS) Indian investigators can interrogate David Headley, said a US official Saturday adding that the Pakistani-born Lashkar-e-Taiba operative's extradition to India was still possible, but not on charges of the 2008 Mumbai terror attacks.

'With respect to the Headley case, the plea bargain agreement was announced and part of that agreement was that the US would not extradite Headley either to India or Pakistan or Denmark for the charges for which he has now admitted guilt,' US Assistant Secretary of State for South and Central Asia Robert O. Blake told reporters here.

Asked if Indian investigators would be allowed to quiz him, Blake said: 'My answer would be yes.'

Blake ruled out Headley's extradition to India on the charges the LeT operative has also pleaded guilty after entering into a bargain with US prosecutors that he would be spared the death sentence or being extradited to foreign countries where he had plotted attacks on behalf of the terror outfit.

The US official, however, left the option open of extraditing Headley if India comes up with cases other than his role in the 26/11 mayhem that left 166 Indians and foreigners dead.

'That does not mean that at some future date, some additional charges could not be brought. I do not want to speculate much on the future charges, but at least on these charges he cannot be extradited,' Blake said.

The US official disagreed when he was asked why the US was not cooperating with India on the Mumbai terror investigations.

'(The) cooperation is exceptional,' he said, adding the two countries would continue making progress on anti-terror ties.

'Home Minister P. Chidambaram had a very successful visit to the US and as a result of that visit we are proceeding in a number of directions to expand our consultations on specific cooperation,' he said, adding that security and intelligence agencies of the two countries have had a 'wide web of exchanges'.

'We are very satisfied on the significant progress that has been made. I cannot speak for the Indians, but I am sure they are as well,' he said.