Elite soldiers fought Isis militants during night-time raid to free US journalist and other hostages, but failed to locate them

Elite US military forces secretly invaded Syria recently in a risky and ultimately unsuccessful attempt to free US journalist James Foley before he was killed by Islamic State (Isis) militants, the Pentagon announced on Wednesday.

Confirmation of the failed night-time raid, which took place earlier this summer, came after a day of sharp questioning over whether the Obama administration had done enough to save Foley's life. It represented the first confirmation of US military operations within insurgency-wracked Syria, where Isis gestated into the jihadist organisation that has redrawn the borders of the Middle East.

The raid involved dozens of special operations forces from all US military services, including the 160th special operations aviation regiment. US forces flew into Syria in defiance of air defence batteries that senior military officials have described as highly threatening to pilots. Modified Black Hawk helicopters were involved, and "armed fixed-wing aircraft and drones" provided cover to forces on the ground, said an administration official.

Yet the operation, which took place in an area of Syria that officials declined to disclose, failed when "the hostages were not present at the targeted location," said rear admiral John Kirby, the Pentagon press secretary.

Special operations forces got into a "firefight" with Isis forces, an official said, killing "several" of them. It took an unspecified amount of time for them to determine that the hostages were not at the scene, prompting a rapid departure. "They were shot at as they were egressing. One person had a minor injury," the official said.

The official said that Isis "did not know who they were fighting that night, and we assess Syria did not know" about the secret incursion.

It is unclear how many hostages the elite troops, which Kirby called "the best of the United States military," attempted to free. At least one other US journalist, Steven Sotloff, is known to be in Isis custody. Disclosure of the unsuccessful operation may have consequences for Sotloff, whom Isis has threatened to kill unless the US ends its bombing campaign against it.

US officials said on Wednesday there was concern about Sotloff after he appeared in the same Isis propaganda video depicting Foley's murder. US warplanes struck Isis vehicles and weaponry near the Mosul dam on Wednesday in tacit defiance of the Isis threat.

With Sotloff's fate an open question, Kirby said in a statement: "The United States will not tolerate the abduction of our people, and will work tirelessly to secure the safety of our citizens and to hold their captors accountable."

White House counter-terrorism adviser Lisa Monaco added: "Our thoughts and prayers are with the remaining hostages' families and their loved ones during this difficult time."

It is also unclear whether the intelligence on the hostages' location was fundamentally flawed or perishable by the time of the raid. Monaco said the US had "what we believed to be sufficient intelligence" justifying the strike.

Robert Caruso, a navy intelligence veteran, said Isis and similar organizations "lie about where they are, where they're going to be in two hours, and they definitely don't talk about it on the telephone."

Caruso also questioned the wisdom of releasing information about the raid.

"It's pretty cavalier for the administration to condemn Snowden and turn around and endanger the remaining hostages. That's not Opsec [operational security]. I've taught it, to the military and the state department. That's not Opsec," he said.

The US official, who was not cleared to speak for the record, acknowledged the risk of the disclosure to Sotloff.

"There is concern that releasing this jeopardises the hostages that remain, but a number of news outlets got ahold of these details and were going to run with this story," the official said, saying that the administration was withholding significant details.

French journalist Nicolas Henin has described how he had spent seven months in captivity with Foley in Syria, including a week during which they were handcuffed together.

Henin, who was released in April this year, told the BBC he felt the UK and US governments were putting their people at risk by not negotiating with the terrorists, and that Foley, as an American, was "some kind of scapegoat" for the terrorists.

Henin said Foley had coped better than others with the conditions in captivity but had also been treated differently. "Being an American he was probably more targeted by the kidnappers. Well, he would be beaten a bit more probably, he was some kind of scapegoat," he told the BBC.

"Some countries like America but also like the UK do not negotiate and, well, they put their people at risk."

Henin paid tribute to his former colleague and friend, saying he had been generous with other captives if they were cold or hungry. He said he was horrified by Foley's killing but would focus on positive memories from their time together.

"I will try to just remember few, very few opportunities we had to laugh loud together – and it did happen actually a couple of times," he said.

The Press Association contributed to this report