However, U.S. counterterrorism officials say signs point to Lashkar-e-Tayyiba, and they haven't seen anything to rule it out.

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Indian authorities believe all the attackers were Pakistanis, specifically blaming Lashkar-e-Tayyiba (LeT), an Islamic militant group based in Pakistan.

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Al Qaeda operative Abu Zubaydah, for instance, was arrested at the home of a Lashkar-e-Tayyiba leader in Pakistan in 2002.

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Besides conducting numerous terrorist operations in India, Lashkar-e-Tayyiba has international reach.

CNN: Commentary: How U.S. should respond to Mumbai attacks

The move comes after the Pakistani government banned his group, Jamaat-ud-Dawa (JuD), a charity affiliated with Lashkar-e-Tayyiba (LeT) which India blames for last month's Mumbai attacks.

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The list includes Hafiz Mohammed, the head of Lashkar-e-Tayyiba.

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At the center of India's probe was the lone suspect in police custody, who Indian authorities say is Pakistani and was trained by Lashkar-e-Tayyiba -- a Pakistan-based terror group allied with al Qaeda.

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Tahawwur Rana, 52, was convicted in June 2011 of conspiracy to provide material support in the plot against the Morgenavisen Jyllands-Posten newspaper and of providing material support to the Pakistan-based Lashkar-e Tayyiba-terror organization.

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Until January of 2002, when it was officially banned following the attack on the Indian Parliament, Lashkar-e-Tayyiba maintained 2, 200 offices around the country and attracted hundreds of thousands of followers to its annual gatherings.

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Zarar Shah, a top operational commander of Lashkar-e-Tayyiba, and Zakir Rehman Lakhvi, whose arrest had been reported Tuesday, were among the militant figures rounded up in recent days, Prime Minister Yousuf Raza Gilani told reporters.

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The acknowledgment came three days after Pakistani security forces raided an LeT camp near Muzaffarabad, the capital of Pakistani-controlled Kashmir, in the first sign of government action against Lashkar-e-Tayyiba since the three-day siege of India's financial capital.

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Reinares, of Madrid's Elcano Royal Institute, said that according to information passed to Spain by several Western intelligence agencies, Megomedov joined training camps in Afghanistan and Pakistan, including camps run by Pakistani militant group Lashkar-e-Tayyiba, after leaving the Russian special forces outfits.

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U.S. Director of National Intelligence Michael McConnell said during an appearance Tuesday at Harvard University said the Mumbai attacks were carried out by the same group responsible for the parliament attack and a series of bomb explosions aboard trains and at railway stations in Mumbai in 2006 -- though he didn't specifically name Lashkar-e-Tayyiba.

CNN: Rice heads to India to ease tensions

The official also noted a possibility that Pakistan-based groups such as Lashkar e-Tayyiba or Tehrik-i-Taliban Pakistan could be involved.

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