CHICAGO: The leadership of Pakistan's ISI spy agency was not involved in planning the deadly 2008 Mumbai attacks, self-confessed plotter David Coleman Headley testified Tuesday.

Headley, who has pleaded guilty to 12 terror charges arising out of the attacks on India's financial capital, said during the Chicago trial of his childhood friend, Tahawwur Hussain Rana, that no more than a handful of ISI agents were involved in the plot.

“The colonel might have known and someone in the group might have known,” Headley testified.

But when asked by Rana's defense attorney if he meant that neither the head of the ISI nor its senior leadership were involved Headley testified “Yes.”

The Mumbai attacks, in which 166 people were killed, stalled a fragile four-year peace process between India and Pakistan, two South Asian neighbors and nuclear-armed rivals, which was only resumed in February.

Pakistan's powerful Inter-Services Intelligence (ISI) agency has long been suspected of involvement and three ISI agents were named as co-conspirators by US prosecutors.

However, Headley's testimony supports Pakistan's assertion that the ISI's involvement was limited to a handful of rogue agents.

Rana is accused of providing Headley with a cover and acting as a messenger, with prosecutors alleging he played a behind-the-scenes logistical role in both the Mumbai attacks and another abortive plan to strike Copenhagen.

Rana, a Canadian-Pakistani and Chicago businessman, has denied all charges, and his defense attorneys argue that he was duped by his friend, whom he had met in military school.

The Mumbai attacks also left more than 300 people wounded after coordinated strikes on high-profile targets by 10 heavily armed extremists.