The US investigators believe some elements in Pakistan's ISI could be linked to American terror suspect David Headley, who is currently in FBI custody for trying to plot attacks in India.
The investigators made this assessment on the basis of the arrest of "two key persons" in Pakistan, sources said. Illyas Kashmiri, a former Pakistani military officer who has become a militant commander associated with both Al-Qaeda and Lashkar-e-Toiba (LeT), is one among them.
They have also zeroed in on a Pakistani national who is suspected to be a key link between LeT handlers and Headley and his Pakistani-Canadian associate Tahawwur Hussain Rana, the sources added.
The sources said India is expected to know in a week from the US whether Headley and Rana, who are operatives of LeT, were involved in Mumbai attacks. Agencies in India have been suspecting that the duo could have been involved in 26/11.
The sources said there is no evidence so far to link the duo with the Mumbai attack.
India and the US are in constant touch on the Headley case and Washington has conveyed that within a week there could be "authentic" information whether they were involved in the attack, the sources added.
A Pakistani national believed to be a common link between the LeT handlers like Zaki-ur Lakhvi and the two terror suspects detained by the FBI has been identified and probe on him is expected to reveal whether Headley and Rana had any role.
The national, whose identity has been kept secret, is believed to have been in Pakistan at the time of Mumbai carnage.