In pursuance of a Supreme Court order, the NIA on Friday registered an FIR to probe the conversion of a young Hindu woman from Kerala to Islam and her subsequent marriage to a Muslim man in 2016, an official said.
The NIA probe will be supervised by retired apex court Justice RV Raveendran.
The case was earlier probed by the Kerala Police under Section 57 of Kerala Police Act, and dealt with charges of promoting enmity between different groups on grounds of religion, malicious acts intended to outrage religious feelings, and abetment of the Indian Penal Code.
An apex court bench of Chief Justice Jagdish Singh Khehar and Justice DY Chandrachud on Wednesday ordered the National Investigation Agency (NIA) to probe the case, wherein the Kerala High Court had annulled the marriage by terming it a "love jihad".
The Kerala High Court, on May 25, had declared as "null and void" the marriage of 24-year-old Hadiya, known as Akhila before conversion, with Shafeen Jahan in December 2016 and ordered for placing her in her parents' protective custody.
Jahan, 27, moved the top court against the High Court order, contending the ruling was an "insult to the independence of women in India".
Jahan claimed Hadiya, a homeopathy student in Kerala, converted to Islam of her own volition two years prior to their marriage and sought direction to Hadiya's father to present her in court.
Hadiya's father, however, said she was a "helpless victim" and trapped by a "well-oiled racket" which used "psychological measures" to indoctrinate people and convert them to Islam.
The father had claimed his daughter had been radicalised by some organisations and they had influenced her to marry a Muslim man, adding that there could be a conspiracy to send her to Syria to work for extremist organisations such as the Islamic State since the man she married had been working in the Gulf.