NEW DELHI: An opposition activist has filed a petition in India's top court challenging the communications blackout and security clampdown in the Indian-controlled portion of Kashmir, where people remained holed up in their homes for a fourth day.

State-run All India Radio says security agencies have arrested more than 500 people in the region apparently to prevent any outbreak of violence.

India's government this week revoked the special status of Jammu and Kashmir and downgraded the Himalayan region from statehood to a territory. Muslim-majority Kashmir is claimed in full by both India and Pakistan, and rebels have been fighting Indian rule in the portion it administers for decades.

India's National Security Adviser Ajit Doval visited Kashmir on Wednesday to assess the law and order situation.