Nayeem and Naseem were questioned earlier on August 8. The elder son Nayeem is a surgeon by profession, while Naseem is an employee of the Jammu and Kashmir government.
According to officials, who are not authorised to speak to media, the two were asked to bring certain documents related to financial transactions that have come under the scanner of the NIA.
Nayeem is tipped as the natural successor to lead the Tehrek-e-Hurriyat, a separatist conglomerate comprising pro-Pakistan hardline groups, after his 87-year-old ailing father.
It had registered the case on May 30, accusing separatist and secessionist leaders of being in cahoots with terrorist groups.
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The case also included causing disruption in the Valley by pelting security forces with stones, burning schools, damaging public property and waging war against India.
It was the first time since the rise of militancy in the early 1990s that a central probe agency conducted raids in connection with the funding of terrorist and separatist groups.
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