American investigators who questioned Ajmal Amir Iman Kasab [Images], the lone terrorist captured during the Mumbai attack, are convinced he is a Pakistani national and that the terrorist strike was planned and executed by the Lashkar-e-Tayiba, diplomatic sources said on Tuesday.

Investigators from the Federal Bureau of Investigation were given access to Kasab for nine hours and after questioning him, they came to the conclusion that he was a Pakistani national as contended by Indian authorities, the sources told PTI.

The sources, familiar with the probe being conducted by the Federal Bureau of Investigation's team dispatched to Mumbai, said American investigators were also convinced that the Mumbai attacks were intricately planned and directed by LeT leaders based in Pakistan.

"The investigators believe the attacks were planned, coordinated and directed from Pakistan by LeT leaders," a source said.

These findings fit in with comments by top American leaders like Secretary of State Condoleezza Rice [Images] and Admiral Mike Mullen, the senior-most US military official, who have asked Pakistan to take quick action against 'non-state actors' based on Pakistani soil who were linked to the Mumbai attacks.

Though Prime Minister Yousuf Raza Gilani [Images] has ruled out allowing the British police to quiz the suspects Pakistan had detained in connection with the Mumbai attacks, the diplomatic sources said it would be hard pressed to take such a stance if the FBI made a similar request, as India had already given American investigators access to Kasab.

The diplomatic sources also provided other details of the FBI investigation that had convinced the US of the complicity of the LeT in the terrorist strike.

American investigators were able to extract details of calls made by the terrorists involved in the Mumbai attacks to their LeT handlers in Pakistan by using sophisticated Technology, to examine the burnt and damaged mobile phones of the attackers, the sources said.

These phones, which were damaged in gun battles between the terrorists and security forces, were provided to the FBI team by Indian law enforcement agencies, they said.

The US dispatched an investigating team to Mumbai as six Americans were among the 183 people killed in the attacks.

Kasab was captured shortly after he and another terrorist struck at a major railway terminus in India's financial hub.

Indian officials said he was a member of the LeT and belonged to Faridkot village in Pakistan's Punjab province.

Kasab's father subsequently admitted to a Pakistani newspaper that the gunman whose pictures were beamed around the world by the media was his son.

Other residents of Faridkot have said that Kasab last visited the village about five to six months ago, when he told his mother he was going away for 'jehad'.

The Pakistan government has said it is awaiting information and evidence from India to confirm the identity and nationality of Ajmal.

The sources also said the FBI investigators had found no evidence of linkages between the 26/11 attacks and the Inter Services Intelligence.