The vehicle with explosives found near industrialist Mukesh Ambani's residence in south Mumbai had been stolen last week, and a letter found inside said this was only a "glimpse" of things to come, police said on Friday.

The National Investigation Agency (NIA) has also started a parallel probe and contacted the Mumbai police crime branch, a senior official said here.

A Scorpio with around 2.5 kg of gelatin sticks was found parked on Carmichael Road near 'Antilia', the multi-storey residence of Ambani, the chairman of Reliance Industries, on Thursday evening.

There was no assembled explosive device with detonators and batteries inside, police said.

CCTV footage showed that the SUV was parked there in the early hours of Thursday, and its driver left in an Innova which had accompanied it to the spot.

"The owner of the vehicle (Scorpio), Hiren Mansukh, visited the police commissioner's office in south Mumbai this afternoon after he saw visuals of the SUV found near Ambani's house, which was similar to his vehicle," the police official said.

Mansukh, a resident of neighbouring Thane, told reporters that he had parked the SUV near Airoli Mulund Bridge on February 17 after its steering got jammed while he was on his way to attend a family function.

"The next day, when I went to get my car, it could not be found....following which I lodged a complaint at Vikhroli police station," he said.

Besides gelatin sticks, a letter was also found in the SUV, in Hindi but written in English alphabet and purportedly threatening Ambani, his wife Nita and the family, police said.

This was only a "Jhalak" (glimpse) but the next time the "saaman" (explosives) will be fully assembled, the letter said.

The letter had several misspellings, which seemed to be an attempt to masquerade the writer's identity, the official said, adding that police were as yet clueless about the intention behind the act.

The letter was in a blue bag next to the driver's seat, while the gelatin sticks were kept in a packet with the name of its manufacturer, "Solar Industries, Nagpur". Also, a bag with `Mumbai Indians' printed on it was found in the car.

Satyanarayan Nuwal, the owner of Solar Industries, said in a statement on Friday that he received a phone call from Mumbai police about the discovery of the packet.

As provided under the Explosives Rules 2008, all the data of production and sale of explosives by the company is submitted to the Explosives Department and police, it said.

Mumbai police have formed at least 10 teams to probe the case.

Police found that there were four number plates in the Scorpio, two of them matching the registration numbers of cars in the Ambani family's security detail.

The number plate fixed on the Scorpio's exterior matched the registration number of the lead car in Nita Ambani's convoy, the senior police official said.

The Innova spotted near the parked SUV on Carmichael Road was first seen entering the city from Thane around 1.20 am on Thursday in a CCTV footage.

As it headed for south Mumbai, the Scorpio joined it near Priyadarshani Park, and both cars then traveled together towards Antilia, CCTV footage showed.

Minutes after stopping on Carmichael Road around 2.15 am, the driver of the Scorpio stepped out and sat in the Innova. The Innova then left and was seen returning to Thane through Mulund check post around 3.05 am.

After that its track was lost, the official said.

On Thursday morning, traffic police even attached a clamp to the Scorpio parked near Ambani's house as it was in no-parking zone and generated an electronic fine receipt, but it did not arouse further suspicion then, the official said.

The number plate of the Innova was also found to be fake, and it too seemed to have been stolen, the official said.

The chassis number of the Scorpio car was found to have been scraped off.

The police said an FIR was registered in connection with the seized SUV at Gamdevi police station against unidentified persons under IPC sections 286 (negligent conduct with respect to explosive substance), 506(2) (criminal intimidation; and section four of the Explosive Substances Act (punishment for attempt to cause explosion).

Reliance Industries in a statement thanked Mumbai Police for "quick and immediate action". "We are confident that Mumbai Police will complete their thorough investigation quickly," it added.