LeT, blamed for the Mumbai attacks, has expanded its operations to Afghanistan and the West and has become more active throughout the region, which calls for concerted action against the outlawed group, America's top military official said on Saturday.
"I've watched LeT (grow) since the end of 2008, move to the West, become more active in other countries, more active throughout the region, more engaged with other terrorist groups,"
Mullen, who arrived in Pakistan on Saturday to meet with the leadership and military officials, said during an interaction with a group of journalists here.
Besides expanding to the West, the LeT "is in Afghanistan (and) other countries", Mullen said in response to questions.
He said there is "heightened concern about (LeT's) emergence and what is significant (is its) emergence not only on the regional stage but potentially as a terror organisation with global aspirations".
"There is an increased level of concern where the LeT is and where it appears to be headed. It is something we all have to address," he said.
Mullen initially tried to parry a question on whether he had raised America's concerns about the LeT with Pakistan's leadership by saying that everyone would have to work together to address the threat posed by the group.
In response to a pointed question on the same issue, Mullen indicated he had raised the matter with the Pakistani leadership on more than one occasion.
"I tried to make the case that the LeT is a growing threat, it is an organisation that is becoming more lethal. (This has been) proven so and it is not just operating where it used to be. It's expanding, it is in the West, it is in Afghanistan, it is in other countries. All of us have to be concerned about it," he said.
India says Pakistan-based LeT, which was founded by terrorist leader Hafiz Muhammad Saeed, was behind the 2008 Mumbai carnage and wants Islamabad to take action against terror emanating from its soil against India.
The LeT, which was banned during the tenure of former military ruler Pervez Musharraf, re-emerged as the Jamaat-ud-Dawah. The JuD, which is also headed by Saeed, was banned by the UN in the wake of the Mumbai attacks.
Replying to another question, Mullen said the US believed top Al Qaida leaders, including Osama bin Laden and Aiman al-Zawahiri, are in Pakistan.
The presence of these terrorist leaders in the region is a reason why "a principal part of the overall Af-Pak strategy is focussed on eliminate safe havens" for them, he said.