(CNN) -- A group calling itself the Deccan Mujahideen has claimed responsibility for Wednesday's coordinated and deadly attacks in southern Mumbai, India, but security analysts know next to nothing about the group, and some discount its claim.
One of the gunmen is pictured in Mumbai, India, during the deadly attacks.
Intelligence officials from India and beyond are trying to determine who the attackers were and what their motivation was. The attacks left at least 125 people dead and more than 300 injured at a handful of sites across Mumbai.
"Deccan Mujahideen seem to be this amazing group that has come out of nowhere, that has been operating under the radar for all this time, yet able to mount such a sophisticated and well-coordinated attack," security analyst Will Geddes told CNN. And that, he suggested, is unlikely.
One highly placed intelligence official who has been briefed on the attacks said that the head of the operation is a Bangladeshi and that the militants are Indians, Kashmiris and Bangladeshis. The Indian military has sustained a large number of casualties, the source said.
A U.S. counterterrorism official said the level of sophistication in the attack leads officials to believe that it might be tied to Lashkar-e-Tayyiba (Army of the Pure), an Islamic extremist group that has carried out previous attacks in India. Watch CNN's Phil Black look at who may be behind the attacks »
LeT, as the group is known, is thought to have been responsible for a string of bombs that ripped through packed Mumbai commuter trains and platforms in July 2006, killing more than 200 people.
The group denied involvement in the attacks Thursday.
"The LeT has no links with Deccan Mujahideen," a caller identifying himself as Abdulla Ghaznavi, an LeT spokesman, told CNN. He said the group condemns the Mumbai attacks and demands an international inquiry into them. iReport.com: Are you there? Send photos and video and share your story
The U.S. State Department says Lashkar-e-Tayyiba has several thousand members in the Pakistan-controlled part of Kashmir and calls it one of the three largest and best-trained groups fighting against India.
Kashmir, divided between India and Pakistan and claimed by both, has been wracked by an 18-year separatist campaign that authorities say has left at least 43,000 dead. Watch: Analyst says 'don't jump to conclusions' »
The counterterrorism official mentioned another group, Jaish-e-Mohammed, which is based in Pakistan and, like LeT, fights for the end of Indian rule in Kashmir. The use of fighters with handheld weapons and grenades against fixed targets would be the type of attack either group would be capable of conducting, the official said.
What is different is the deliberate targeting of Westerners, the official said.
A senior U.S. official said, "our attention is focused on the sophistication of the execution of the attacks." Watch a witness describe the scene »
The sophistication was "to the extent it does not seem like Deccan Mujahideen could carry it off, so the question is, did they have outside help?" the source asked.
Both U.S. sources, meanwhile, said the attacks do not seem to point to al Qaeda, which usually launches mass-casualty attacks using vehicles or suicide vests and does not usually take hostages.
Another group being mentioned as a possible culprit is the Indian Mujahideen, a Muslim militant group that emerged about a year ago. Despite its relatively new status, the organization is thought to have the organizational capability to carry out such attacks, said Paul Cruickshank, a fellow at the Center on Law and Security at New York University's School of Law.
The group has declared "open war" against India in retaliation for what it said were 60 years of Muslim persecution and the country's support of U.S. policies.
In September, the group said it was behind a series of explosions that ripped through busy marketplaces in New Delhi, killing 24 people and wounding about 100. The group also claimed responsibility in May for near-simultaneous bomb attacks that killed 63 people in the northwest city of Jaipur.
Officially, the Indian government has said no one has claimed responsibility for this week's Mumbai attacks. The Deccan Mujahideen claims came in e-mails to several Indian media outlets.
Deccan refers to the Deccan Plateau, which makes up the majority of the southern part of the country. "Deccan" is an Anglicized form of "dakkhin," which means south. Read more on the international reaction
Mujahideen translates into "those engaged in the struggle for jihad." Although "jihad" in Islam can mean any endeavor that requires dedication, the term has taken on a militant tone in recent years.
Indian Prime Minister Manmohan Singh suggested in a television address that the attacks were launched by people from outside the country.
"It is evident that the group which carried out these attacks, based outside the country, had come with single-minded determination to create havoc in the financial capital of the country," Singh said.
Indian security experts agree that the attackers came from outside the country.
"What you're seeing is that these types of attacks are established. There's a network. There's well-planned reconnaissance and logistics and financial support. It could only be from a group that's receiving international support, obviously with a domestic dimension," terrorism expert Sajjan Gohel said.
"This time, there was a multipronged approach. It wasn't just about targeting Indians. It was an aim, but it wasn't the only one," Gohel said. "They also wanted to go after Westerners, as well. They wanted to create a lack of confidence in people traveling to India, hit at the economy, hit at the tourism industry."
Fingers have also been pointed toward Pakistan, India's neighbor. The two nations, both nuclear powers, have a tense relationship.
"It's everybody's right to say what they want to say, but as far as my country is concerned, we are already hit by this terrorism," Pakistani Prime Minister Yousuf Raza Gilani told CNN's Reza Sayah. Watch the Pakistani PM condemn the attacks »
"I think this is a heinous crime, and we condemn it," Gilani said. "And I think this terrorism is a menace for the whole world, and therefore we have to work jointly to combat terrorism and extremism."
Husain Haqqani, Pakistan's ambassador to the United States, released a statement saying that terrorism "is a threat to both India and Pakistan."
"Pakistan has vehemently condemned the terrorist attacks in Mumbai. It is unfair to blame Pakistan or Pakistanis for these acts of terrorism even before an investigation is undertaken," Haqqani's statement reads. "Instead of scoring political points at the expense of a neighboring country that is itself a victim of terrorism, it is time for India's leaders to work together with Pakistan's elected leaders in putting up a joint front against terrorism."
CNN's Nic Robertson contributed to this report.