Khurram Parvez, 39, coordinator of the Jammu Kashmir Coalition of Civil Society (JKCCS) has long campaigned against human rights violations committed by state forces in the volatile Himalayan region of Jammu and Kashmir.
His arrest in September was condemned by human rights groups, as well as the United Nations, who said Parvez's detention was a deliberate attempt by Indian authorities to obstruct his work.
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The Jammu and Kashmir High Court quashed the detention order against Parvez saying police had exploited their position and did not have enough evidence to detain the activist.
"What emerges is that the detention of (Parvez) is not only illegal but the detaining authority has abused its powers in ordering his detention," said an order by Justice MH Attar.
Police officials declined to comment on the court order and were unwilling to confirm if they would release Parvez.
The JKCCS has published research into the role of Indian security forces in containing an insurgency in Kashmir that first flared a quarter of a century ago.
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Parvez was stopped by authorities at New Delhi airport on Sept. 14 when he was on his way to Geneva to attend the UN Human Rights Council.
He is currently being held in preventive detention under the highly controversial Jammu and Kashmir Public Safety Act, which allows for people to held for up to two years without judicial intervention.
But the court said that allegations such as that he was inciting people who were coming out of a mosque to shout slogans were not backed up with any proof.
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Dozens of civilians have been killed and thousands wounded in months of clashes between protesters and security forces in Kashmir state, sparked by the killing of a leading separatist militant in a joint army and police operation in July.
The unrest is the worst in the Muslim-majority region for six years, and critics have accused Indian forces of heavy-handedness as they struggle to contain the protests.
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