"The Commission has observed that it appears the standard operating procedure in connection with these arrests has not been properly followed by the police, which may amount to violation of their human rights," the NHRC said in the notice to state DGP Datta Padsalgikar and the Chief Secretary.

The NHRC has asked them to file their replies within four weeks.

It pointed out that earlier it had received a complaint from a Geneva-based NGO pertaining to the illegal arrests of five rights activists in June, some of whom were also raided in April.

Following the arrests (in June), the NHRC had issued a similar notice to the state government on June 29, but the latter has not submitted its report yet.

Tuesday's arrests of lawyer-activist Sudha Bharadwaj, civil liberties activists Gautam Navlakha, Vernon Gonsalves, Arun Fereira and poet-activist Varavara Rao from different parts of India, triggered a massive outcry.

As in June, the arrests were made in connection with the ongoing investigations into the January 1 caste riots in Koregaon-Bhima, Pune district and a subsequent complaint lodged in the matter.

Besides, police raided another eight activists across the country, including Kranti L.C., Fr. Stan Swami, and Anand Teltumbde, in the major operation as part of the ongoing probe into the involvement of Maoist supporters into the Koregaon-Bhima riots.

Officials described Tuesday's operations as a 'follow-up' to similar action taken in April-June when the Pune police swooped on over half a dozen Dalit activists and those involved with the Kabir Kala Manch, which organised an Elgar Conference in Pune on December 31, 2017.

The next day, on January 1 (2018), caste riots erupted in Koregaon-Bhima which left one person dead, culminating in a Maharashtra shutdown on January 3 called by the Bharipa Bahujan Mahasangh, headed by Prakash Ambedkar, grandson of B.R. Ambedkar.