At least three Mumbai-based men who joined Isis are set to return from Iraq as Indian security agencies are perplexed over how they can be charged as the men have not committed any crimes in their home country.

One of the Islamist radicals, Shaheen Tanki, was in telephonic contact with his family ever since he reportedly joined Isis in May.

"For the time since he went missing, Shaheen [Tanki] spoke to his mother and brother. He said he's perfectly fine and they should not worry about him," a family member, who did not wish to be identified, told the Times of India.

Tanki, who went missing along with three others, all of them in their early twenties, reportedly joined the Sunni militant group.

It is not known what prompted the men to decide to return to India or when they will be back.

"Since the outfit [Isis] they are allegedly working for is not banned in India, no action can be taken against them," a source from a security agency told the newspaper.

Another source from the Anti Terrorism Squad said: "We have no intention to prosecute them. However, their statements will be recorded and information on how they reached, who guided them will be extracted. It's still not clear whether they joined Isis or not. We don't have any evidence for this too."

There were reports earlier which said the Indian federal government had asked security agencies to tighten the screws on anyone who had joined or wished to join Isis after it emerged that nearly 22 Indians had joined the insurgent group in Iraq.