ISLAMABAD, Pakistan—Hafiz Saeed, the leader of a Pakistani Islamist group linked to a deadly attack in India in 2008, was put under house arrest Monday.

Mr. Saeed was detained in the eastern city of Lahore, where he lives, officials said. His Jamaat-ud-Dawa group is accused by New Delhi, Washington and the United Nations of being behind the multiday terrorist strike in the Indian city of Mumbai, which killed 166 people. The group has denied involvement in the attack.

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