Updated

Pakistan said Tuesday it will boycott an upcoming meeting in Germany on the future of Afghanistan to protest the deadly attack by U.S.-led forces on its troops, widening the fallout from an incident that has sent ties between Washington and Islamabad into a tailspin.

Meanwhile, a top Pakistani army general called the incident Saturday that killed 24 troops on the Afghan-Pakistan border a "deliberate act of aggression" by NATO forces and said the military had not decided whether to take part in an American investigation into it.

Both developments bode ill for future Pakistani cooperation with U.S. and NATO forces in Afghanistan, and point to the hardline being taken by the army, which is under pressure by an anti-American public to respond forcefully. NATO has described the incident as "tragic and unintended", and U.S. officials have expressed their sympathies with the families of those who died.

The decision to skip the conference in Bonn, Germany, which has been a year in the planning, will trigger concerns in Washington and Kabul that Pakistan is withdrawing from international efforts to stabilize Afghanistan before and after the withdrawal of foreign combat forces in 2014.

It was taken during a Pakistani Cabinet meeting in the city of Lahore, said three officials who attended the meeting. They spoke on condition of anonymity because they were not authorized to talk to the media ahead of an official announcement.

Pakistan, which has long had a troubled relationship with Washington, has already closed its western border to trucks delivering supplies to NATO troops in landlocked Afghanistan and said it will review all cooperation with NATO and the United States.

The Dec. 5 Bonn meeting was to bring together Western and regional leaders to forge a strategy to stabilize Afghanistan and smooth the planned American withdrawal from the country in 2014.

Pakistan is perhaps the most important regional country because of it influence on Afghan Taliban factions on its soil, and U.S. and Pakistani officials had been urging Islamabad to attend.

Given the general pessimism about the future of Afghanistan, few had high expectations the conference would result in significant progress. But the absence of Pakistan will make even minor achievements much more difficult.

There have been conflicting versions of what led to the attack by NATO aircraft on Saturday, though most Afghan and Western accounts say it was likely a case of friendly fire, launched after a joint Afghan and U.S. special forces team received fire from the Pakistan side of the border.

But Pakistan army Gen. Ashfaq Nadeem called the incident a "deliberate act of aggression" Tuesday and said it was "next to impossible that NATO" did not know they were attacking Pakistani forces. Nadeem made the remarks to a briefing of Pakistani news anchors, senior journalists and defense analysts in army headquarters.

Foreign media were not invited, but two attendees relayed to The Associated Press what Nadeem said.

One was analyst and retired Gen. Talat Masood; the other didn't give his name because he feared his employers might not approve.

Nadeen said the army had little faith that any investigation will get to the bottom of the incident and may not cooperate with it. He said other joint inquiries into at least two other similar, if less deadly, incidents over the last three years had "come to nothing."

Pakistan is understandably angry over the death of its soldiers, but its leaders appear to be playing up their outrage to satisfy the demands of the already intensely anti-American public. It also seeks fresh leverage in the relationship with Washington, which despite the mistrust, neither side wants to break entirely.

Anthony Cordesman, an analyst for the Center for Strategic and International Studies in Washington, said it's likely that this crisis "will get papered over" with some sort of U.S. or NATO apology and a " bribe in the form of better aid flows."

"In the process, however, the U.S. will face even less prospect that Pakistan will really crack down on insurgent groups in the border area, or stop seeing Afghanistan as an area where it competes with India and which is useful for strategic depth in some future war with India," said Cordesman.