India's intelligence agencies investigated the series of terror attacks in Mumbai (formerly Bombay) on Thursday as officers continued to fight pockets of gunmen throughout the city. It is still not clear if the terrorists responsible for the attack came from Pakistan or from within India.

While initial investigations suggested the terrorists had infiltrated India from Pakistan, later information suggested that a group calling itself “Deccan Jihad” was responsible. Deccan is a majority-Muslim area in Mumbai.

Indian defense officials said the Deccan Jihad group was unknown. The group may be new, or the offspring of an established terrorist group, they said.

Experts in India and the United States suggested that the Indian Mujahideen may have been involved. The India-based group first became well-known approximately one year ago, when it declared war on India for what it called anti-Muslim persecution and support for the U.S. It has murdered dozens in previous terrorist attacks, including an attack in May that killed 63.

Indian Mujahideen is not the only terrorist group capable of mass-casualty attacks, however. Experts also suspect the Army of the Pure terrorist group, which murdered over 200 people in the Mumbai train station in 2006. The Mumbai train station was one of the locations targeted in Wednesday and Thursday's attack.

Analysts said that whoever the terrorists were, they were apparently targeting India's tourist industry, as some of Mumbai's top tourist destinations were attacked and dozens of foreigners were among the dead, wounded and kidnapped.

Singh vows to fight back

Prime Minister Manmohan Singh spoke to the nation on Thursday and vowed to do whatever possible to prevent future attacks. India will stop the flow of money to terrorists and prevent suspects from entering the country, he declared. “We will pursue these people and these groups, we promise that anyone who initiates, organizes or supports terrorism, no matter what his affiliation or religion, will pay a heavy price for his cowardly and terrible actions against our people,” Singh said.

Singh said India would turn to “neighboring countries” and tell them India will not tolerate the use of their territory to launch terrorist attacks. “There will be a price if they do not take appropriate steps,” he said.

While Singh did not specify a neighboring country suspected of housing the terrorist group responsible for the attack, analysts said he was referring to Pakistan. Pakistan has frequently been accused of inciting anti-India sentiment among India's roughly 150 million Muslims.

Pakistani leaders denounced the Mumbai attacks on Thursday and called for joint Pakistani-Indian efforts to fight regional terrorism.

Schweitzer: Expect similar attacks

Yoram Schweitzer of Israel's Institute for National Security spoke with Arutz Sheva on Thursday and said the Mumbai attacks were unusual due to the use of hostage taking. Muslim terrorist groups do not usually take hostages, he said.

Schweitzer warned that the attack in Mumbai could be followed by similar attacks. When a method of attack proves effective, it tends to be quickly imitated by Muslim terrorist groups worldwide, he said.