Indian authorities have extended the detention of two former Occupied Kashmir chief ministers, held for the past six months under a security clampdown, using a law allowing for them to be locked up for two years without charge, police said Friday.

Mehbooba Mufti and Omar Abdullah, despite having long supported Kashmir being part of India, were detained in August when New Delhi rescinded the region's autonomy and imposed a vice-like security and communications lockdown.

Facing international unease, Prime Minister Narendra Modi said the move was to bring peace to a region where tens of thousands have died in a three decade old uprising against Indian rule.

Freedom fighters have been fighting some 500,000 Indian forces in the territory, demanding independence or to join Pakistan which also controls part of the Himalayan region.

Mufti and Abdullah's provisional detention expired on Thursday and they were immediately booked under the Public Safety Act (PSA), a police source in Kashmir told AFP.

The legislation was used against a third former chief minister Farooq Abdullah, the father of Omar Abdullah, in September to keep the 82-year-old under house arrest.

The PSA was introduced in the 1970s to prevent timber smuggling in Kashmir but since the uprising erupted in 1989 it has been used to detain thousands of people, activists say.

The UN human rights office in 2018 criticised special laws in Kashmir including the PSA saying they "impede accountability and jeopardise the right to remedy for victims of human rights violations".

Mufti's daughter Iltija Mufti slammed use of "the draconian PSA" by the government. "Question is how much longer will we act as bystanders as they desecrate what this nation stands for?" she said on Twitter.

Dozens of other politicians and others including lawyers, trade unionists and activists also detained in August, some of them in prisons all over India, have been released gradually in recent weeks.

Restricted Internet access was allowed in late January after a blackout lasting almost six months that Modi's government had said was imposed for security reasons, but which has hit hard the economy, healthcare and education.

However Kashmir's more than seven million inhabitants can still only access a "whitelist" of 301 government-approved websites that do not include social media. Cellphone data is only possible on slower second-generation (2G) connections.