The NIA did not name anyone in its press release but said it has “arrested a key conspirator who confessed his involvement in the criminal conspiracy of the train blast”.

The announcement comes a day after India and Pakistan agreed on anti-terrorism cooperation — that includes sharing probe information on the Samjhauta blast and the 2008 Mumbai terror attack.

The home ministry said in a statement that the “conspirator has also divulged names of co-conspirators, who had caused the blasts and further investigation is continuing”. The agency said the accused was arrested in December last year.

The NIA claim comes on the day when Pakistani Prime Minister Yousuf Raza Gilani watched the World Cup semifinals between the sub-continental rivals in Mohali on the invitation of his Indian counterpart Manmohan Singh.

At the home secretary-level talks here on Tuesday, India had conveyed to Pakistan that it would share the findings of the Samjhauta blast probe after the investigation is completed.

In January, in a confessional statement before a magistrate, Rashtriya Swayamsevak Sangh (RSS) leader Swami Aseemanand had conceded that he and other Hindu activists were involved in the train blast and bombings at Muslim religious places because they wanted to answer every “Islamist terror act” with “a bomb for bomb” policy.

The NIA said the success in the case was achieved after “painstaking investigation” on the blast in the Samjhauta Express, a peace train between India and Pakistan.

The investigation was done “in a number of states, at different locations and also involved experts from the forensic science and railways,” it said.