Americans fighting the war in Afghanistan have long harbored strong suspicions that Pakistan’s military spy service has guided the Afghan insurgency with a hidden hand, even as Pakistan receives more than $1 billion a year from Washington for its help combating the militants, according to a trove of secret military field reports made public Sunday.

The documents, made available by an organization called WikiLeaks, suggest that Pakistan, an ostensible ally of the United States, allows representatives of its spy service to meet directly with the Taliban in secret strategy sessions to organize networks of militant groups that fight against American soldiers in Afghanistan, and even hatch plots to assassinate Afghan leaders.

Taken together, the reports indicate that American soldiers on the ground are inundated with accounts of a network of Pakistani assets and collaborators that runs from the Pakistani tribal belt along the Afghan border, through southern Afghanistan, and all the way to the capital, Kabul.

Much of the information — raw intelligence and threat assessments gathered from the field in Afghanistan— cannot be verified and likely comes from sources aligned with Afghan intelligence, which considers Pakistan an enemy, and paid informants. Some describe plots for attacks that do not appear to have taken place.

But many of the reports rely on sources that the military rated as reliable.

While current and former American officials interviewed could not corroborate individual reports, they said that the portrait of the spy agency’s collaboration with the Afghan insurgency was broadly consistent with other classified intelligence.

Some of the reports describe Pakistani intelligence working alongside Al Qaeda to plan attacks. Experts cautioned that although Pakistan’s militant groups and Al Qaeda work together, directly linking the Pakistani spy agency, the Directorate for Inter-Services Intelligence, or ISI, with Al Qaeda is difficult.

The records also contain firsthand accounts of American anger at Pakistan’s unwillingness to confront insurgents who launched attacks near Pakistani border posts, moved openly by the truckload across the frontier, and retreated to Pakistani territory for safety.

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