The measure, which Mr. Modi’s Bharatiya Janata Party had promised during the election campaign this year, permanently incorporates the territory that it controls into the rest of India.

Ahead of the announcement, India flooded the disputed region with thousands of extra troops, evacuated tourists, closed schools and cut off internet service.

Explainer: When India and Pakistan won independence in 1947, the Muslim-majority princely state of Kashmir opted to remain independent. But militants from Pakistan soon invaded, prompting Kashmir to seek protection from India. It agreed to become a part of India under certain conditions set out in Article 370.

Reaction: Pakistan, opposition lawmakers in India and some analysts denounced the move as potentially illegal and likely to end up before India’s Supreme Court.