Police said that they have leads and will soon solve the case.
A day after a rocket-propelled grenade or RPG was fired at its intelligence wing headquarters in Mohali, the Punjab Police on Tuesday said it has recovered the launcher used in the attack and that a number of suspects have been rounded up.
Chief Minister Bhagwant Mann said the strictest punishment will be meted out to those trying to spoil the state's atmosphere.
Director General of Police (DGP) V K Bhawra said they have got a few leads and the case will be solved soon.
"A number of suspects have been rounded up and questioned. The launcher used in the attack has been recovered by the police and all leads developed in the case are being pursued meticulously," a statement issued by the Mohali police said.
The rocket-propelled grenade was fired at the third floor of the highly-guarded building in Mohali's Sector 77 at 7:45 pm on Monday, following which an alert was sounded in Punjab.
A case under the relevant sections of the Indian Penal Code (IPC), the Unlawful Activities (Prevention) Act (UAPA) and the Explosives Act has been lodged at Mohali's Sohana Police Station in connection with the incident.
The case was registered on the basis of the statement of sub-inspector Balkar Singh, the security in-charge of the intelligence wing headquarters.
In his statement, the sub-inspector said that he heard the sound of an explosion on the third floor of the building and when he went there, he saw smoke coming out of room number 41.
He said a projectile, after hitting the wall and breaking the window panes, hit the roof of the room before falling on a chair.
Earlier in the day, the chief minister held a meeting with the DGP and top officials of the intelligence wing and directed the state police chief to probe the matter thoroughly.
Mann said nobody would be allowed to disturb the peaceful atmosphere in Punjab, adding that a few inimical forces are constantly trying to foment trouble across the state, but they will never succeed in their nefarious designs.
During the meeting, the DGP apprised the chief minister that a few suspects have been taken into custody for interrogation.
"Some arrests have been made and more will be made," Mr Mann said after the meeting, apparently referring to the people who have been rounded up for questioning.
"Whoever tries to spoil the atmosphere of Punjab will not be spared and the strictest punishment will be given to them, which their coming generations will remember," the Chief Minister said.
Later, after a meeting with senior officials at the intelligence wing headquarters, Mr Bhawra told reporters in Mohali that a projectile had hit the building and the explosive used in it seems to be TNT (trinitrotoluene).
"There was nobody in the room when the incident occurred. The impact was on the wall," he said.
"But it is a challenge and we are making all-out efforts to solve the case," the DGP added.
To a question on whether it was a terror attack or there was a Khalistani angle in it, Mr Bhawra said whatever comes out of the investigation, "we will let you know".
"We have leads and we will soon solve the case," he said.
A preliminary investigation pointed towards the involvement of two men who came in a car and fired the RPG at the building.
The incident is being seen as a major intelligence failure, as the building houses the state counter-intelligence wing, the special task force, the anti-gangster task force and some other units.
Police also suspect the involvement of gangster-turned-terrorist Harvinder Singh Rinda, who is believed to be in Pakistan, in the incident.
Rinda has been taking the help of local gangsters to carry out anti-national activities here, police sources said.
His name figured when a terror plot was foiled recently with the arrest of four suspected Pakistan-linked terrorists in Haryana's Karnal. Rinda's involvement was also detected in a hand-grenade attack at the Crime Investigation Agency (CIA) office in Nawanshahr last month.
The incident took place days after the arrest of the four suspected Pakistan-linked terrorists in Karnal and the arrest of two people that led to the recovery of an Improvised Explosive Device (IED) packed with 1.5 kg RDX from Punjab's Tarn Taran district.
The explosion also came close on the heels of the recovery of an explosive device near the Burail Jail in Chandigarh on April 24.
Delhi Chief Minister and Aam Aadmi Party (AAP) national convener Arvind Kejriwal said the explosion was "a cowardly act" and his party's government in Punjab will ensure that the culprits get the "strictest punishment". Meanwhile, the opposition parties described the incident as "disturbing" and "shocking".
Congress MLA and Leader of Opposition in the Assembly Partap Singh Bajwa said the attack was worrying and posed a threat to the hard-earned peace in the state.
"RPG attack on Punjab Police intelligence wing office in Mohali is worrying. This after RDX was found few days back in Tarn Taran. Punjab has been through dark times already, we can't afford to damage the hard-earned peace of Punjab," Mr Bajwa said in a tweet.
Punjab BJP chief Ashwani Sharma said the blast at the building of the intelligence headquarters is a matter of concern and expressed surprise over the local police describing it as a "minor" explosion.
The Mohali Police had on Monday said a minor explosion was reported at the headquarters.
"The Chief Minister needs to pay attention to the deteriorating law and order situation in Punjab," Mr Sharma said in a tweet.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)