Delhi Police probing a possible Khalistani link in the blast near a CRPF school here on Monday wrote to messaging app Telegram to know the details of a group that claimed responsibility of the explosion, police sources said on Monday.

A strong blast ripped through a wall of the CRPF school in Rohini's Prashant Vihar area on Sunday morning. No one was hurt in the blast but a signboard, hoardings of nearby shops and window panes of vehicles parked near the spot were damaged in the incident.

In its FIR filed on the incident, a copy of which has been accessed by PTI, police has mentioned a "white powder found scattered" at the site and said the explosion was caused by "unknown explosive substance".

Meanwhile, police sources also said they have recovered CCTV footage of a suspect from the night before the incident.

A purported Telegram post circulated on social media, which claimed that the blast was carried out in retaliation to the "targeting" of pro-Khalistan separatists allegedly by Indian agents.

The post surfaced on social media late on Sunday evening pointing to the possible involvement of pro-Khalistani separatists behind the blast.

"The police has written to Telegram to the know details of the creator of the group - Justice League Indian - in which the CCTV of the blast was shared with a Khalistan Zindabad watermark on it," a police source said.

A Telegram post by "Justice League India" read, "If Indian coward agency and their master think they can hire filthy goons to target our members to silence our voice then they live in fools world. They can't imagine how close we are to them and how capable we are to strike anytime #KhalistanZindabad #JLI."

A team of Central Reserve Police Force (CRPF) visited the spot on Monday morning.

Sources said police has recovered a CCTV in which a suspect in white T-shirt is spotted on the spot, a night before the blast.

It is suspected that an Improvised Explosive Device (IED), wrapped in a plastic bag, was hid in a one-feet-deep pit near the CRPF school wall, they said.

The teams of Delhi Police Special Cell, Crime Branch and local police are investigating the case.

An FIR under Sections 326(g) (mischief with severe consequences to public safety) of Bharatiya Nyaya Sanhita, Prevention of Damage to Public Property Act and Explosives Act was registered at Prashant Vihar police station.

The FIR stated that there had been a "loud noise accompanied by white fumes of smoke" near the outer boundary wall of the CRPF Public School on Lancer Road.

A hole, caused by the blast, in the boundary wall of the school is evident, the FIR said.

Window panes and signboards of shops opposite the CRPF school were damaged due to the blast's impact, it said.

During the inspection, white powder was found scattered near the site, the FIR said. Samples of "white powder" and soil collected from the spot were sent to the laboratory to ascertain the bomb's composition.

The explosion was caused by an unknown explosive substance, it added.

On Sunday, the Forensic Science Laboratory (FSL) and National Security Guard (NSG) teams inspected the spot and collected samples.

NSG commandos also deployed robots to scour the area for more explosive materials. "The white powder could be a mixture of ammonium nitrate and chloride," a senior police officer said.

The officer said the perpetrator "intentionally" selected the spot to not harm the people but to send a message.