Pakistan's military on Monday rejected U.S. findings on a November 26 NATO cross-border air attack that killed 24 Pakistani soldiers, reducing the chances of a resolution of the dispute and an improvement in ties which are at their lowest in years.

Pakistan does not agree with several portions and findings of the investigation report, as these are factually not correct, the military said in a statement after a detailed review of the U.S. investigation.

The U.S. report released on December 22 found both American and Pakistani forces were to blame for the incident near the Afghan border, inflaming already strained ties.

Affixing partial responsibility of the incident on Pakistan is therefore unjustified and unacceptable, said the Pakistani military.

The U.S. military said it stood 100 percent behind its investigation and Captain John Kirby, a Pentagon spokesman, noted that Pakistan declined to participate in the American probe.

Pakistan responded to the attack by shutting down ground routes to supply U.S.-led NATO forces in Afghanistan and forced the United States to vacate an air base used to launch drone flights.

This is going to affect the relationship. The relationship was already in the doldrums, it was in bad shape. I don't know if it has the capacity to get any worse, said Mahmud Durrani, a retired Pakistan army major general.

It's very unusual because normally allies fight side by side.

Last week, a senior Pakistani security official told Reuters the routes would be reopened, but heavy tariffs would be imposed.

The fundamental cause of the incident of 26th November, 2011, was the failure of U.S./ISAF (International Security Assistance Force) to share its near-border operation with Pakistan at any level, said the Pakistani military.

The death of the Pakistani soldiers dug in along the mountainous, isolated border area, along with the initial NATO response, has incensed Pakistanis and marked yet another setback in the Obama administration's efforts to improve chronically troubled ties with an uneasy ally.

The U.S. military blamed Pakistani soldiers for firing at NATO forces as they prepared for a mission in the remote corner of eastern Afghanistan.

The U.S. investigation also conceded a critical error by U.S. troops, who told Pakistan the cross-border shooting was taking place about 9 miles (14 km) away due to mapping error. Pakistan responded by saying it had no troops there.

Pakistan admitted that its posts engaged in speculative fire, including the use of mortar bombs, which the U.S. interpreted as hostile fire.

But it denies that it fired in the direction of the Afghan and NATO forces and was instead firing at suspected militant movement.

(Additional reporting by Rebecca and Chris Allbritton in Islamabad and Phil Stewart in Washington; Writing by Michael Georgy; Editing by Sanjeev Miglani and Cynthia Osterman)