CPI-M has expressed serious concern over Indian investigating agencies not being allowed to interrogate LeT operative David Coleman Headley and sought to know what steps the government is taking into the matter.

Raising the issue during Zero Hour in Rajya Sabha on Tuesday, party member Brinda Karat said Headley, earlier a drug smuggler, worked as an undercover agent of the US intelligence agency CIA since 1999 and the US government helped him make frequent trips to Pakistan. (Read: David Headley: US agent who went rogue?)

He even travelled to India after the Mumbai blasts. FBI was aware of Headley's antecedents even before Mumbai blasts, she said adding, "We want to know did FBI pass on real time intelligence to Indian agencies."

Karat asked why Indian investigators were denied access to Headley when FBI was allowed to interrogate Ajmal Kasab, the lone terrorist caught alive in 26/11 attacks.

"Did our Prime Minister raise the issue with the US President," she asked. She also wanted to know what steps are being taken to ensure that Indian investigators question Headley at the earliest.

A number of members associated with her on the issue.