The reports had warned that there could be a possible entry of terrorists into Mumbai through the sea route, a top police official claimed.

"This intelligence was available six months ago and subsequently a barge was found by the locals on Shrivardhan coast in Raigad district four months back," the official, who did not wish to be identified, said.

Locals feared that the barge might have contained explosives but nothing was found when customs and naval personnel inspected it.

The terrorists, who created havoc in Mumbai overnight, came by boats, Chief Minister Vilasrao Deshmukh has said.

Militants armed with automatic weapons and grenades attacked Taj and Oberoi hotels, hospitals and a famous tourist cafe in Mumbai late on Wednesday, killing more than 100 people.

* WHO IS BEHIND THE ATTACKS?

Witnesses say the attackers were young South Asian men speaking Hindi or Urdu, suggesting that they are probably members of an Indian militant group rather than foreigners.

The attacks were claimed by a previously unknown group calling itself the Deccan Mujahideen in an e-mail to news organisations. Deccan is an area of southern India.

Analysts say that while it is not clear whether the claim is genuine, the attacks were most likely carried out by a group called the Indian Mujahideen. The name used in the claim of responsibility suggests the attackers could be members of a south Indian offshoot or cell of the Indian Mujahideen.

* WHO ARE THE INDIAN MUJAHIDEEN?

Indian police say the Indian Mujahideen is an offshoot of the banned Students' Islamic Movement of India (SIMI), but that local Muslims appear to have been given training and backing from militant groups in neighbouring Pakistan and Bangladesh.

SIMI has been blamed by police for almost every major bomb attack in India, including explosions on commuter trains in Mumbai two years ago that killed 187 people.

Police said the Indian Mujahideen may also include former members of the Bangladeshi militant group Harkat-ul-Jihad al Islami.

* WHY ARE THEY SUSPECTED OF BEING BEHIND THE MUMBAI ATTACKS?

The Indian Mujahideen have made credible claims of responsibility for most of the recent major attacks on civilian targets in India over the past two years.

The Mumbai attacks appear to have been carefully co-ordinated, well-planned and involved a large number of attackers. A high level of sophistication has also been a hallmark of previous attacks by the Indian Mujahideen.

The Mumbai attacks also focused clearly on tourist targets, including two luxury hotels and a famous cafe.

In May, the Indian Mujahideen made a specific threat to attack tourist sites in India unless the government stopped supporting the United States in the international arena.

The threat was made in an e-mail claiming responsibility for bomb attacks that killed 63 people in the tourist city of Jaipur. The e-mail, signed by "Guru Al-Hindi", declared "open war against India" and included the serial number of one of the bicycles on which the bombs were left.

Witnesses in Mumbai say the attackers in Mumbai singled out Americans and Britons in their attacks.

* WHAT OTHER ATTACKS HAVE INDIAN MUJAHIDEEN CARRIED OUT?

The group first emerged during a wave of bombings in the northern state of Uttar Pradesh in November 2007, sending an e-mail to media outlets just before some of the bombs exploded.

Their next attacks were the Jaipur blasts.

On July 25, eight small bomb attacks in the IT city of Bangalore on July 25 that killed at least one person and wounded 15. There was no known claim of responsibility.

But a day later, at least 16 bombs exploded in Ahmedabad in the state of Gujarat, killing 45 and wounding 161. Shortly before the blasts, an e-mail in the name of the Indian Mujahideen was sent to local media warning that people would soon "feel the terror of death" in the name of Allah.

It said the attacks were revenge for the Gujarat riots of 2002, when around 2,500 people, most of them Muslims, were killed by Hindu mobs. A later e-mail accused several state governments of harassing, imprisoning and torturing Muslims and threatened consequences if they did not stop.

In September, at least five bombs exploded in crowded markets and streets in New Delhi, killing at least 18 people.

The Indian Mujahideen sent out an e-mail moments after the first blast in New Delhi, saying the explosions were to prove its capability to strike in the most secure of Indian cities.

* WHAT WAS DIFFERENT ABOUT THE MUMBAI ATTACKS?

All previous incidents in which the Indian Mujahideen are suspected of involvement involved co-ordinated serial bombs.

The Mumbai attacks also show clear signs of coordination but were carried out by gunmen, some carrying grenades.

The tactics -- a military-style assault on soft targets, singling out foreigners, and taking hostages -- is rare and does not fit the usual methods of militant attacks on civilian areas.

However, similar attacks have been carried out before, notably the May 2004 attacks in the eastern Saudi city of Khobar.

Gunmen attacked two oil industry installations and a foreign workers' housing complex in the city, taking more than 50 hostages and killing 22 of them. The attackers asked hostages whether they were Christian or Muslim before deciding whom to kill.