A 21-year-old environmentalist has been arrested in India after allegedly using social media to mobilise support for protesting farmers by sharing a campaign “toolkit” promoted by Swedish activist Greta Thunberg.

Disha Ravi, a leader of the Indian arm of Thunberg’s Friday for Future campaign movement, was taken from her home in Bangalore on Saturday and flown to New Delhi for police interrogation for suspected sedition.

Civil rights activists and human rights lawyers say the young woman’s arrest reflects New Delhi’s increasingly tough approach to dissent and criticism.

Authorities are investigating what they say is an international conspiracy against the Indian government, after Thunberg wrote a tweet showing her support for the protesting farmers and providing a link to the toolkit.

India’s foreign ministry hit out at “sensationalist social media hashtags and comments” by celebrities after Thunberg and pop singer Rihanna posted tweets about the protests.

Delhi police said in a tweet on Sunday that Ravi “is a key conspirator” in developing and disseminating the toolkit, which they have described as “a call to wage economic, social, cultural and regional war against India”.

Police say Ravi developed the guide, which offered advice on how to support the farmers’ protests, and shared it with Thunberg. They also accuse Ravi of collaborating with Sikh separatists “to spread disaffection against the Indian state”.

In a court appearance on Sunday, Ravi was remanded in police custody for five days for questioning.

New Delhi is also engaged in a tense stand-off with Twitter over demands that the social media site block hundreds of accounts the government alleges have sought to instigate unrest, including journalists, news publications, activists and opposition politicians.

Ravi’s detention has prompted alarm among activists and lawyers. “To accuse a young climate activist of sedition — even if it’s true that she had some part in a social media ‘toolkit’ — is deeply egregious,” said Karuna Nundy, a Supreme Court lawyer. “This comes at a time when those who disagree with government policy are being systematically targeted for saying so.”

“Going after perhaps the youngest and most vulnerable of the activists sends out a chilling message,” she added.

TM Krishna, a prominent classical musician, said in a tweet that, “if arresting a 21-year-old environmental activist for social media toolkit is not a sign that we have descended into police state territory, I don’t know what is”.

Farmers have been protesting for months against three new laws that are intended to deregulate India’s tightly controlled agricultural markets. Thousands have set up camp on the outskirts of New Delhi, representing the biggest political challenge to Narendra Modi since he became prime minister in 2014.

Farmers fear that the new rules — which will allow companies to buy directly from farmers — are a step towards ending government procurement of crops at fixed prices, leaving them vulnerable to corporate exploitation.

New Delhi, however, alleges the protests are being fomented by overseas Sikh separatists, who want to create an independent homeland called Khalistan in Punjab state.

The Sikh separatist movement wracked India in the 1980s and caused many deaths, including the assassination of former prime minister Indira Gandhi, but the campaign largely petered out decades ago.

Analysts say linking the protests to a separatist movement has allowed authorities to use tougher tactics, including a British colonial-era sedition law under which those convicted can face life in prison.