ISLAMABAD -- U.S. officials gave Pakistan soldiers the wrong location when asking for clearance to attack militants along the border last weekend, Pakistani military officials said Friday.

The strike resulted in the deaths of 24 soldiers and a major crisis in relations between Washington and Islamabad.

The claim was the latest in a series by mostly anonymous officials in both countries, which try to explain what happened before and during last Saturday's bombing of two Pakistani border checkpoints by U.S. aircraft.

NATO and America have expressed regret for the loss of lives, but have rejected Pakistani descriptions of the incident as a deliberate act of aggression.

The incident has pushed already strained ties between Washington and Islamabad close to rupture, complicating American hopes of securing Pakistan's help in negotiating an end to the Afghan war. In retaliation for the raid, Islamabad has already closed its eastern border to NATO supplies traveling into landlocked Afghanistan.

Thousands of Islamist extremists and other demonstrators took to the streets across the country after Friday prayers to protest the strike. Some called on the army to attack the U.S.-led coalition in Afghanistan. The chants were a worrying sign for the West, indicating that anger over the incident is uniting hard-liners and the military.

U.S. officials have told The Associated Press that Saturday's incident occurred when a joint U.S. and Afghan patrol requested backup after being hit by mortar and small arms fire by Taliban militants.

Before responding, the patrol first checked with the Pakistani army, which reported it had no troops in the area, they said.

U.S. officials say that Pakistani troops had "given the go-ahead" for the strikes, The Wall Street Journal reported on Friday. This account would suggest that the Pakistanis were at least partly to blame for the deadly error.

A Pakistani military official who spoke on condition of anonymity because of the sensitivity of the information confirmed that the American had provided his side with a location for the planned strike.

However, he said, the information arrived late, Pakistan never cleared the strike, and the coordinates provided were incorrect anyway.

"Wrong information about (the) area of operation was provided to Pakistani officials a few minutes before the strike," he said. "Without getting clearance from Pakistan side, the post had already been engaged by U.S. helicopters and fighter jets."

He said that U.S. officials at the border coordination center, where the two sides liaise over operations close to the frontier, had later "apologized privately to Pakistani officials for initially providing wrong information and the subsequent engagement of the post without prior information."

The U.S. and NATO have both launched investigations. Only when investigators have spoken to people on both sides of the border will they be able to describe the full version of events.

This assumes that the two sides can work together. The ongoing anonymous back-and-forth claims and denials by officials on both sides appear to reflect bad blood between them.

Washington has not formally apologized, saying it would not be appropriate before an investigation into the incident is complete.

Anti-American demonstrations took place around Pakistan on Friday, including a 2,000-strong rally in the country's commercial hub of Karachi by the Sunni extremist Sipah-e-Sahaba group.

The group is banned because of its ties to al-Qaida, but that ban is largely ignored.

Aurangezeb Farooqi, a leader of the group, asked the protesters whether they were ready to join the army to fight Americans. Many raised their fists in response and shouted "God is great!".

Some held up placards saying: "There is only one treatment for America: jihad, jihad," or holy war.

Washington believes that Islamabad's cooperation is vital to negotiate a truce with Afghan insurgent leaders based on Pakistani soil, so that the U.S. can withdraw most of its troops from Afghanistan by the end of 2014.

But Islamabad has its own interests, chiefly in ensuring that whatever regime remains in Kabul after U.S. forces withdraw is friendly to Pakistan, and hostile to India. Consequently, Pakistan appears to be in no rush to take political risks helping the United States.