"We are very much engaged in this question whether ISI had any connection with the Mumbai attack or not," said a senior Administration official.
The official, who requested anonymity, said that the matter was under investigation and he would not like to comment till the probe was over.
Beside the interrogation of Pakistani-American LeT operative David Headley, India's own investigation also had disclosed the role of ISI in the Mumbai attacks.
US top officials had told Pakistan that it 'must' take strong action against those involved in the Mumbai terrorist attacks.
"The message has been delivered quite forcefully and quite convincingly," said US official.
He also added that Pakistan must recognize that it is contrary to their own interests for the future and the stability of the region to continue to tolerate the existence of insurgents within their borders.