He told parliament on Thursday evening that even though a police investigation into the case was still ongoing "all indications point to an Indian module".
No one has claimed responsibility for the July 13 rush-hour bombings that ripped through the Opera House diamond trading hub, Zaveri Bazaar gold and jewellery quarter and the suburban district of Dadar.
It is for the first time that the government has pointed towards the involvement of a home-grown terror group for the three explosions in the metropolis.
But suspicion has fallen on the Indian Mujahideen, a shadowy group of domestic militants that have carried out similar attacks in the past, including in the capital
New Delhi and the western city of Ahmedabad in 2008.
The Indian Mujahideen is believed to have links with the Pakistan-based Lashkar-e-Taiba.
Indian blamed the attacks on the LeT and suspended a peace dialogue with arch-rival Pakistan that only formally resumed earlier this year.
Chidambaram told lawmakers that India was not exempt from the rise of militant forces across the world, as opposition leaders accused the minister of being soft on extremism.
He accepted that domestic extremists threatened the country's unity and recognised that the Pune blast in 2010 and the latest attack in Mumbai were "two major blots" on the counter-terrorism fight.
Mr. Chidambaram said that there was considerable improvement in the intelligence machinery both at the State and at the Central level.