The Pakistani army has rejected a US investigation that concluded mistakes on both sides led to US air strikes last month that killed 24 Pakistani soldiers and severely damaged the already strained relationship between the two countries.

The response indicates the report will do little to ease tensions, a worrying development for the US because Pakistan's co-operation is critical for its conduct of the Afghan war. The Pakistani army has said its troops did nothing wrong and claimed the attack was a deliberate act of aggression.

Pakistan has retaliated by closing its Afghan border to supplies meant for Nato troops in Afghanistan and kicking the US out of a base used by American drones. Nato officials have said the closure of the supply route has not affected operations so far, but will eventually if not reversed.

The Pakistani army said it "does not agree with the findings of the US/Nato inquiry as being reported in the media", in a short statement on Friday. "The inquiry report is short on facts," it added.

The army would provide a detailed response after officials received the report, it said. Pakistan refused to co-operate in the investigation.

Even though US officials on Thursday accepted some of the blame for the attack on two army posts along the Afghan border and expressed regret for the deaths, they did not apologise for the incident, as many Pakistanis have demanded. Instead, the US said its forces were fired on first from the direction of the posts and acted "with appropriate force" in self-defence.

Brigadier General Stephen Clark, an air force special operations officer who led the investigation, also said in a Pentagon briefing that US forces did not know that the two relatively new Pakistani outposts – spare structures constructed with stacked gray stones – had been set up on the border.

The Pakistanis have disputed both of these points, saying their troops did not fire first and that they had given Nato maps that clearly marked where the outposts were located on a mountain ridge in the Mohmand tribal area.

Clark said the heavy machine gun and mortar fire continued even after an F-15 fighter jet and an AC-130 gunship flew over, shooting flares in a "show of force" to signal the presence of American or Nato troops. Taliban insurgents fighting in the area do not have aircraft.

"This is key for the ground technical leader's mindset, in that there should be no doubt in anybody's mind that it's now coalition forces in the area," said Clark.

He acknowledged that the US had not informed Pakistan that American and Afghan commandos were conducting an overnight operation in Afghanistan on 25-26 November when the attack occurred. US and Nato commanders believed that some of their military operations had been compromised when they had given details and locations to the Pakistanis, he said.

There was "an overarching lack of trust between the two sides" that keeps them from giving each other specific details on troops or combat outpost locations, Clark said, as he went through a blow-by-blow account of the incident.

He also said US forces failed to determine who was firing at them and whether there were friendly Pakistani forces in the area because they used inaccurate maps and mistakenly provided Pakistan with the wrong location where they said fighting was taking place – an area almost nine miles away.

Pakistan could seize on these admissions to lower the temperature on the crisis, but it may be difficult for the army to walk back from the categorical positions it has taken. The attack has enraged the Pakistani public, especially anti-US hardliners. More than 30,000 Islamists staged a rally against the attack on Sunday.

Pentagon officials said on Thursday that military leaders had spoken by phone to Pakistan army chief General Ashfaq Pervez Kayani about the report's conclusions, but had not yet given him a detailed briefing.

In Kabul, defence ministry spokesman Mohammad Zahir Azimi said the Afghan government would not comment on the US report.

The deadly incident was the latest blow to the relationship between Pakistan and the US, which has been hit by a series of crises this year. A CIA contractor shot and killed two Pakistanis in the eastern city of Lahore in January, setting off a storm of anti-American protests.

This anger was compounded by the US raid that killed Osama bin Laden in a Pakistani garrison town in May. The Pakistanis were outraged by the operation because they were not told about it beforehand.