Pakistan's spy agency masterminded the July 11 train bombings that killed more than 200 people in the Indian city of Mumbai, the top police officer in charge of the investigation alleged Saturday.
A Pakistani official rejected the claim, labeling the allegation "sad and unfortunate."
Mumbai police Commissioner A.N. Roy said the attacks were planned by the spy agency and carried out by Pakistan-based Islamic militant group, Lashkar-e-Tayyaba, assisted by the Students Islamic Movement of India, a banned Islamic group.
Addressing a news conference to announce the completion of the investigation, Roy said 15 people had been arrested, including 11 Pakistanis.
Roy said Pakistan's Directorate of Inter Services Intelligence, or ISI, the country's top spy agency, began planning the attacks in March and later provided training to those who carried out the bombings in Bahawalpur, Pakistan.
Pakistan has in the past denied any involvement in the attacks and it was not immediately clear what implications the revelations would have on the fragile peace process between the nuclear-armed neighbors.
Roy gave a detailed description of how the explosives were transported into India and by whom. He also described how the bombs were packed into pressure cookers and placed on the trains.
Seven bombs ripped through suburban trains in Mumbai, India's financial and entertainment capital, killing at least 207 people and injured another 700. Mumbai was formerly known as Bombay.
Lashkar-e-Tayyaba is one of the Islamic groups fighting since 1989 for Kashmir's independence from India or its merger with Pakistan. More than 68,000 people have been killed in the conflict.