The DNA samples of 21 family members of the missing men were collected on the directions of External Affairs Ministry, officials said.
The families told reporters they had no idea why their DNA samples were collected and that the officials did not give them any reason either.
The 39 Indians, mostly from Punjab's Amritsar, Gurdaspur, Hoshiarpur, Kapurthala and Jalandhar districts, went missing in Iraq's Mosul when it was overrun by the Islamic State.
The central government continues to classify the 39 men as "missing".
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