Pakistan's inaction against Lashkar-e-Taeba (LeT) even after David Headley's revelations about Islamabad's collusion in the Mumbai terror attacks is a 'ticking time bomb' for US-Pakistan partnership, a former CIA analyst has warned.

Indians 'have suspected Pakistani collusion in the Mumbai attacks from the start but could not prove it before' Pakistani-American terror suspect David Coleman Headley's 'extraordinary confessions', Bruce Riedel, now a South Asia expert at the Brookings Institution, said in a commentary.

'Headley's revelations, if true, paint a picture of official Pakistani military cooperation in an act of mass causality terror that raises very worrisome and alarming questions about our most important partner and India's nuclear-armed neighbour,' he said.

'The truth about Mumbai and the future of Lashkar-e-Taeba is the ticking time bomb that could wreck the nascent US-Pakistan partnership,' said Riedel, who played a key role in President Barack Obama's review of US Afghanistan policy last year.

'Thanks to David Headley's extraordinary confessions, we now know how thoroughly LeT planned its 2008 Mumbai attack and how closely linked it is to Al Qaeda - and perhaps to the Pakistani military,' he said.

'There is no excuse for not executing a more robust crack down on Lashkar-e-Taeba and its front organisations from the Pakistani government and for not conducting a thorough house cleaning within the Pakistani army,' Riedel said.

During her recent visit to Kabul, US Secretary of State Hillary Clinton also mentioned that Headley's comments have included 'a revealing set of facts' which the US has now shared with the Pakistanis, he noted.

'Washington and New Delhi are both now waiting for Islamabad to respond,' Riedel said.

'The Indians who have resumed their official dialogue with Pakistan after suspending it in the wake of 26/11 seem uncertain about how to proceed next.'

According to Headley's own confession, he was intimately involved in every aspect of the planning for the Mumbai attacks, and then went on to work with LeT and Al Qaeda on a plot to attack Denmark, Riedel noted.

Headley also reportedly told his Indian interrogators that Pakistani intelligence paid for the boat that took the 10 terrorists from Karachi to Indian waters and that Pakistani naval frogmen had provided intensive commando training for them.

(Arun Kumar can be contacted at arun.kumar@ians.in)