Addressing a press conference here, Uttar Pradesh Director General of Police (DGP) O.P. Singh said, "A joint team of UP and Gujarat Police has detained Maulana Mohsin Sheikh, Faizan and Khurshid Ahmed Pathan and is interrogating them."

Singh said the police initially detained five persons from Surat, but two were released later. "Their activities are being monitored," said Singh.

The National Investigation Agency (NIA) is also keeping an eye on the probe and the may soon take over the probe from the UP Police soon.

According to Gujarat Police sources, the attackers wearing saffron clothes, had walked into Tiwari's office in Khurshid Bagh on Friday on the pretext of handing over a box of sweets. Inside the office, the assailants opened the box, took out a gun and sprayed bullets at Tiwari and fled. Tiwari was rushed to the hospital but could not be saved.

Tiwari, a former Hindu Mahasabha chief, had in January 2017 formed the Hindu Samaj Party and was known for making controversial remarks. In 2015, he was arrested and the National Security Act (NSA) was slapped on him after he made some controversial statement about Prophet Muhammad. Recently, the Lucknow bench of the Allahabad High Court revoked the NSA against him.

"In the initial interrogation, no criminal background has been established of the three detained. If needed, we will take them into remand, and bring them to UP for questioning," said the DGP.

He said, "In the FIR, two people -- Maulana Anwarul Haq and Mufti Naeem Qazmi -- were named as conspirators. These two have also been detained and they are being questioned."

Asked if the murder had any links with terrorist organisations, Singh said: "So far no link with any terrorist organisation has been established. We are looking into all the angles."

To a question over the reason behind Tiwari's murder, Singh said, "Prima facie, these people were radicalised by the speech that he (Tiwari) gave in 2015, but much more can come out when we catch hold of the remaining criminals."

Singh also denied that there were any security lapses on part of the UP Police. "He (Tiwari) was given a gunner and a policeman, both were there with him. There was no laxity on the part of the police administration," he said.

This is the fourth murder of a right wing leader this month in UP. On October 8, BJP leader Chaudhary Yashpal Singh was gunned down in a similar manner in Deoband, while on October 10, BJP leader Kabir Tiwari was shot dead in Basti. Kabir Tiwari was also a former student leader and student groups went on a rampage after his killing, burning down government vehicles.

On October 13, BJP corporator Dhara Singh, 47, was gunned down by unidentified assailants in Saharanpur.

According to NIA sources, two IS suspects arrested by the Gujarat Police in 2017 -- Obaid Mirza and Qasim -- had revealed during interrogation that Tiwari was on their hitlist. The two said that they had been shown a video of Tiwari and asked to eliminate him.

The NIA sources said that the agency was following the case closely and if any indication of participation by any terror group appears, it will take over the probe.