The NIA has arrested absconding Khalistani terrorist Gurjeet Singh Nijjar at the Delhi airport on his deportation from Cyprus for allegedly hatching a criminal conspiracy to revive Sikh militancy in India for a separate state of Khalistan, an official said on Wednesday.

The premier investigation agency had registered a case in January last year against accused Harpal Singh under the Arms Act, the Maharashtra Police Act and the Unlawful Activities (Prevention) Act.

Nijjar, the main conspirator, Harpal and Moin Khan were active on social media platforms and allegedly hatched a criminal conspiracy to revive Sikh militancy with the ultimate aim of the formation of a separate state of Khalistan, a National Investigation Agency (NIA) spokesperson said.

As part of the conspiracy, the three used to post videos and images containing praises of militant Jagtar Singh Hawara (a convict in the assassination of former Punjab chief minister Beant Singh), the Operation Blue Star of 1984, besides pro-Khalistani posts related to the proscribed organisation, Babbar Khalsa International (BKI), with the sole intention to motivate like-minded Sikh youngsters and others to join the so-called Khalistan movement, the official said.

Moin was in Tihar Jail from 2013 to 2016, during which he developed contact with Hawara, showed his willingness to work for him and shared his contact number with him, the NIA spokesperson said.

Subsequently, as planned, Moin sent a friend request to the Facebook ID, "Khalistani Jindabad Khalistan", from his account on the social media platform. Through this Facebook ID, he came in contact with Harpal and Nijjar, the official said.

Nijjar motivated Moin by discussing about the "atrocities committed against Muslims and Sikhs in India and convinced him to work for a separate Khalistan State", he added.

Nijjar directed Moin to purchase a pistol and ammunition in 2018 in order to give effect to their nefarious designs, the official said.

In May last year, the NIA filed a chargesheet in a special NIA court against Nijjar, Harpal, Moin and Sundar Lal Parashar.

Nijjar, who hails from Punjab's Amritsar, left the country in October 2017 for Cyprus. Accordingly, a Look-Out Circular (LOC) was issued against him.

On Tuesday, Nijjar was detained at the Indira Gandhi International (IGI) Airport here and arrested by the NIA.

His transit custody will be obtained to take him to Mumbai for further investigation, the NIA spokesperson said.