The action taken by the Delhi Police on an FIR related to a toolkit shared by climate campaigner Greta Thunberg in support of the ongoing farmer protests has triggered a war of words between the opposition and the ruling BJP.

Accusing the government of "murdering democracy" by using force against a 21-year-old, the opposition on Monday said the voice of India cannot be silenced even as the BJP defended the action, saying a crime is a crime no matter at what age.

Congress leader Rahul Gandhi led the opposition offensive following the arrest of 21-year-old Disha Ravi in the case and said the country will not be silenced.

"Your lips are free to speak. Say that the truth is still alive. They are scared, not the country," he said in a tweet in Hindi.

"India will not be silenced," he added.

Delhi Chief Minister Arvind Kejriwal said, "Arrest of 21-year-old Disha Ravi is an unprecedented attack on Democracy. Supporting our farmers is not a crime."

RJD leader Manoj Jha said democracy is under threat. "I am worried about democracy, as it is passing through the most difficult times," he said.

Union minister and Bharatiya Janata Party (BJP) leader Gajendra Singh Shekhawat tweeted: "If age is the criteria then Param Veer Chakra Second Lt Arun Khetarpal, martyred at 21 is who I am proud of. Not some toolkit propagandists."

BJP general secretary B L Santosh tweeted: "21 year old...environment activist...student...Are these credentials for becoming a part of breaking India forces? How does she get the access for editing tool kit...? Why she is part of anti-national WhatsApp groups...? Many questions...But only one answer...21 year old."

"Bengaluru, Greta Thunberg, Vegan, sole bread winner, student, 21 year old, passionate activist...so many attempts to white wash a sin...!! Not one anarchist ready to answer the question...How 21 year old student got access to edit Toolkit," he asked.

Former Union ministers P Chidambaram and Jairam Ramesh have also come out strongly against the police action in the case, accusing the government of running an authoritarian regime as it was threatened by a student.

"I strongly condemn the arrest of Disha Ravi and urge all students and youth to raise their voices to protest against the authoritarian regime," Chidambaram said.

"The Indian state must be standing on very shaky foundations if Disha Ravi, a 22 year old student of Mount Carmel college and a climate activist, has become a threat to the nation.

"A 'took kit' to support the farmers' protest is more dangerous than the intrusion by Chinese troops into Indian territory. India is becoming the theatre of the absurd and it is sad that the Delhi Police has become a tool of the oppressors," he said in a series of tweets.

Ramesh said, "Delhi Police on the rampage. After Disha Ravi, it is now the turn of another young woman, Nikita Jacob. More will no doubt follow...."

"This is Tanashaahi in New India called Amit Shahi," he said.

"The arrest and the manner of arrest of green activist Disha Ravi shows clearly the intensifying Murder Of Democracy in India. But the young in India cannot be silenced. More power to them," the former environment minister added.

In a tweet in Hindi, Congress general secretary Priyanka Gandhi Vadra said, "The ones with guns are afraid of an unarmed girl. The flames of courage from an unarmed girl have spread." She also used hashtags "ReleaseDishaRavi" and "IndiaBeingSilenced".

Congress leader Rajeev Gowda said an activist who stands up for farmers, fights for the planet is arrested on flimsy grounds.

"Has the government lost its balance? Will not such trumped-up charges, seeing conspiracy in regular social media mobilisation, do more damage to democracy?" he asked.

Reacting to the Opposition charges, BJP spokesperson Gaurav Bhatia said, "A criminal is a criminal, gender and age are immaterial if not a juvenile. Just for your knowledge, Kasab was 21 when he attacked Mumbai."

"Supporting 'farmers' is not a crime but conspiring against India and inciting others surely is," he said.

BJP's IT cell in-charge Amit Malviya said, "The Left has been using young impressionable minds as cannon fodder for their deranged politics for a long time. From JNU to Jamia, AMU to Nadwa and now Disha Ravi, are all part of their sinister plot...Unfortunately they are abandoned soon after they have served their purpose."

The Delhi Police said non-bailable warrants have been issued against two people for allegedly sharing the "toolkit" related to farmers' protests on social media, two days after it arrested climate activist Ravi in connection with the case.

The 21-year-old activist was arrested from Bengaluru on Saturday and sent to five days' police remand by a Delhi court on Sunday.

The two suspects against whom the non-bailable warrants have been issued are Nikita Jacob and Shantanu, the police said, adding that the duo was allegedly involved in preparing the document and was in direct touch with pro-Khalistani elements.