The discovery indicates that Bin Laden used the group, Harakat-ul-Mujahedeen, as part of his support network inside the country, the officials and others said. But it also raised tantalizing questions about whether the group and others like it helped shelter and support Bin Laden on behalf of Pakistan’s spy agency, given that it had mentored Harakat and allowed it to operate in Pakistan for at least 20 years, the officials and analysts said.

In tracing the calls on the cellphone, American analysts have determined that Harakat commanders had called Pakistani intelligence officials, the senior American officials said. One said they had met. The officials added that the contacts were not necessarily about Bin Laden and his protection and that there was no “smoking gun” showing that Pakistan’s spy agency had protected Bin Laden…

“It’s a serious lead,” said one American official, who has been briefed in broad terms on the cellphone analysis. “It’s an avenue we’re investigating.”…

Harakat “is one of the oldest and closest allies of Al Qaeda, and they are very, very close to the ISI,” said Bruce O. Riedel, a former Central Intelligence Agency officer and the author of “Deadly Embrace: Pakistan, America, and the Future of the Global Jihad.”