NEW DELHI (Reuters) - Reports of sexual assault on women in southern India have sparked outrage, with opposition politicians on Tuesday protesting against what they called a lack of progress in the investigation.

The case has received widespread media coverage in Tamil Nadu state weeks before a general election, with opposition parties accusing the state government of “shielding” the perpetrators.

A state minister who often speaks on behalf of the government did not respond to calls and messages seeking comment.

Police in Tamil Nadu said they had arrested four men based on a complaint by an alleged victims, and were investigating if the accused were serial offenders.

The victim, a 19-year old woman, said in a complaint filed with the police that she was traveling with the four men, two of whom she knew, in a car last month when she was forcibly disrobed and videotaped.

She alleged the men then threatened to upload the video online if she did not meet them whenever summoned.

Senior police official R. Pandiarajan said late on Monday that police had recovered four videos from the arrested men, involving other victims. He said numerous women could have been targeted by them, but declined to give specifics.

Police appealed to victims to come forward.

The main opposition party in one of India’s biggest and most developed states, the Dravida Munnetra Kazhagam, held a protest on Tuesday to demand faster action on the case, police said.

The #MeToo movement in India gathered momentum last year with numerous complaints of sexual harassment and other sexual misconduct leveled against prominent journalists, actors, movie directors, comedians and other public figures.