Official sources said Khan was called yesterday to the agency's office here to remain present and render help in "extricating" data from the hardware of the gadgets seized from his premises during a searches conducted by it on February 9, after a gap of two years.
The agency also wanted to take his voice samples to match them with certain audio evidences, they said.
However, Khan's lawyer Prashant Patil told PTI that taking a voice sample of his client was against the law.
He said Khan told investigators that he was "ready to cooperate with them" but they should record his voice sample in "normal conversation mode".
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Agency sources said Khan's statement was not recorded and will be done at a later stage, if required.
Patil said his 61-year-old client was "medically unwell and in a critical condition".
The agency, which has booked Khan and few of his alleged associates under criminal charges of money laundering in 2011, had swooped down on a dozen premises last month in connection with its probe.
The sources said the action (searches on February 9) against Khan and his other associates in the case has come about after a two-year lull as the agency wants to revive the case and bring to light additional evidences so that a trial against him in a Mumbai court could be initiated and the case brought to its logical conclusion.
Khan came under the scrutiny from multiple agencies
including the Economic Offences Wing of the Mumbai Police in 2007 which had been probing him and his associates for charges of money laundering, income tax evasion and violations of the Passport Act.
While the I-T department raised a tax arrear demand of Rs 50,345.73 crore on Khan, ED registered a criminal case of money laundering against him for allegedly stashing away USD eight billion of unaccounted money in foreign banks.
ED has attached few immovable assets of Khan and it is in process to confiscate them soon even as the hearing of the said case in a Mumbai court is scheduled for early next month.