New Delhi: The Centre has registered a fresh FIR against Khalistani separatist leader Amritpal Singh, who has been declared "fugitive" by the Punjab Police, and is likely to take over the investigation as a case of terrorism, media reports said.

The case is likely to be probed by the country’s top anti-terror organisation National Investigation Agency (NIA). The agency will probe Amritpal Singh and seven of his aides over the charge of possessing illegal arms - Arms Act cases are included in the NIA Act, reported NDTV.

The Khalistani leader has been named "Accused Number one" in the new case.

Yesterday, four of Amritpal Singh’s aides were flown to Assam where they have been detained in Dibrugarh Central Jail.

A team of around 30 members from the Punjab Police, including the Inspector General of Prisons, escorted Amritpal Singh’s aides to Assam, the report said.

They were flown from Amritsar to Dibrugarh in an Indian Air Force AN32 aircraft and reached their destination via Assam’s Jorhat. Dibrugarh and Jorhat are both major bases of the Indian Air Force.

The four close aides of Amritpal Singh have been charged under the stringent National Security Act (NSA), which allows the police to detain suspects in any prison across the country, said the report.

The move to transfer the four arrested aides to Dibrugarh was a coordinated action between the BJP-ruled Centre and Assam and AAP-ruled Punjab.

However, Assam Chief Minister Himanta Biswa Sarma said it was just a "police-to-police" cooperation. "There were arrests in Assam as well when we sent people to Bihar's Bhagalpur jail for security reasons. Maybe the Punjab Police feels the prisoners should be held in Assam for a few days," he said, according to NDTV.

Ahead of the operation on Amritpal Singh and his aides, Punjab CM Bhagwant Mann had met Home Minister Amit Shah on March 2 and reportedly discussed the plan to nab the separatist leader.

Mann had also tweeted about the meeting, saying that the Centre and the state have decided to work together on the issues of law and order in the state.

"Today, after meeting the Union Home Minister @AmitShah. We discussed the issue of drones and drugs on the border... The issue of shifting the barbed wire on the border was also discussed... Asked to release Punjab's stalled rural development fund soon... Center-Punjab will work together on the issue of law and order," read a translation of the tweet.

So far, the police have arrested 112 supporters and close aides of Amritpal Singh. Of them, 34 were arrested on Sunday and 78 were nabbed on Saturday.

Police have also detained several members of the 'Waris Punjab De' group for questioning. Among those arrested was Daljeet Singh Kalsi, the man who manages Amritpal Singh's finances.