Pakistan's intelligence agency was behind the train blasts in Mumbai in July that killed 186 people, Indian police say.
Seven blasts hit Mumbai's busy commuter network
The attacks were planned by the ISI and carried out by the Islamist militant group Lashkar-e-Toiba, based in Pakistan, Mumbai's police chief said.
AN Roy said the Students' Islamic Movement of India had also assisted.
Pakistan rejected the allegations and said India had given no evidence of Pakistani involvement in the attacks.
"We have solved the 11 July bombings case. The whole attack was planned by Pakistan's ISI and carried out by Lashkar-e-Toiba and their operatives in India," Mumbai (Bombay) police commissioner AN Roy told a news conference.
Tariq Azim Khan, Pakistan's minister of state for information, rejected the allegations.
"We are still studying the Indian statement. Needless to say, this is once again baseless allegations - yet another attempt by India to malign Pakistan," he told the BBC.
"Both the president and the prime minister condemned this terrorist attack on the train when it happened. But India also must look at home for reasons for this growing insurgency at home," he said.
On 11 July 2006, seven co-ordinated blasts within 15 minutes ripped through trains on Mumbai's busy commuter network.
The Mumbai police chief said the 11 July case was "solved"
Mr Roy said 15 people had been arrested, and that some of the bombers had received training in Pakistan.
He said the bombs were made using a total of 15-20kg of an explosive called RDX, which was smuggled into the country and packed into seven pressure cookers.
Timers were attached to the bombs, which were put into bags and concealed using newspapers and umbrellas, he said.
He said 11 Pakistanis were involved in the operation, and had crossed into India in small groups from Pakistan, Nepal and Bangladesh.
Seven teams, each made up of one Indian and one Pakistani militant, transported the bombs by taxi before placing them on the trains, Mr Roy said.
Indian security officials suggested early on in their investigations that the bombings bore the hallmarks of Lashkar-e-Toiba, a leading militant group fighting in Kashmir and based in Pakistan.
But Pakistan denied any involvement in the blasts and Lashkar-e-Toiba condemned the attacks.
India postponed talks with Pakistan after the bombings, but Indian Prime Minister Manmohan Singh and Pakistani President Pervez Musharraf met recently in Cuba and said they had agreed to resume talks.
The two nations, both nuclear armed, have fought three wars since independence, two over the disputed territory of Kashmir.