India has repeatedly accused its neighbour and arch rival of some degree of involvement in the attacks on its financial capital that killed 166 people and of acting too slowly in arresting those responsible.

The latest tit-for-tat underscores the fragility of ties between the nuclear-armed neighbours despite the resumption of peace talks broken off after the Mumbai attacks and warming trade relations.

However, India on Tuesday emphasised that talks between the Indian and Pakistani foreign secretaries, scheduled for July 4-5 in New Delhi, would go ahead as planned.

Indian police arrested Sayeed Zabiuddin Ansari at Delhi airport on June 21, accusing him of helping coordinate the attack by 10 gunmen of Pakistan's Lashkar-e-Taiba (LeT) militant group from a "control room" in the Pakistani city of Karachi.

"He has confirmed that he was in the control room and he has named a few people who were in the control room," Home Minister Palaniappan Chidambaram said of Ansari, despite the fact he has yet to be charged, let alone found guilty.

"So that confirms our suspicion that it was an organised effort which had some kind of state support. The argument that it was non-state actors who were behind the 26/11 massacre is no longer valid. We've always said that some state support was there for these people."

Indian media reported on Wednesday that members of Pakistan's ISI military intelligence agency were also in the control room at the time of the attack and supplied the plotters with laptops that enabled them to communicate with the attackers via an Internet voice service.

It was not possible to independently verify the information, which was sourced to Indian security officials.

Indian officials have in the past accused members of the ISI of involvement in the Mumbai attacks, although on Wednesday Chidambaram did not directly blame the intelligence agency.

Islamabad swiftly rebutted the latest charge. Rehman Malik, an adviser to Pakistan's prime minister on interior affairs, said there was no record of Ansari having entered the country legally.

"What I am saying is, let's stop the blame game," he told a news conference in Islamabad.

"At that point in time (the Mumbai attacks), Pakistan was blamed, that perhaps the state was involved. But we proved, not only to India, but to the world, that non-state actors were involved, not the state."

Pakistan routinely denies Indian accusations of Pakistani involvement in militant attacks on Indian soil.

Ansari's arrest casts a fresh spotlight on Pakistan's history of backing militant groups as a tool of foreign policy. Pakistan's ISI nurtured the emergence of the LeT in the early 1990s to serve as a proxy to fight Indian forces in Kashmir.

Pakistan denies backing militant groups, but experts believe the security establishment maintains a relationship with LeT.