However US media, citing senior Obama administration officials, said Foley was among those US Special Operations commandos were trying to rescue.

The video of Foley’s killing also showed a second US reporter, Steven Sotloff, being paraded by a black-clad IS militant who warned that he would also be killed if US President Barack Obama does not stop air strikes on IS positions in Iraq.

“The United States attempted a rescue operation recently to free a number of American hostages held in Syria by the Islamic State of Iraq and the Levant (IS),” Pentagon spokesman Rear Admiral John Kirby said.

“This operation involved air and ground components and was focused on a particular captor network within ISIL (IS).

“Unfortunately, the mission was not successful because the hostages were not present at the targeted location.”

The White House said in a separate statement that the rescue attempt was authorised “earlier this summer.”

It involved several dozen US commandos, one of whom was injured in a fierce firefight with IS militants, said, calling it the first known US ground operation in Syria since the country’s descent into civil war.

The said that it was believed that Sotloff was also among the group being held that included Foley.

IS, also known as ISIL, considers Washington its arch enemy and has overrun large swathes of Iraq and Syria.

It says it represents the aspirations of a global Muslim caliphate.

“As we have said repeatedly, the United States government is committed to the safety and well-being of its citizens, particularly those suffering in captivity,” said Kirby.

“In this case, we put the best of the United States military in harms’ way to try and bring our citizens home.”

In the White House statement on the rescue attempt, Lisa Monaco, assistant to President Barack Obama for Homeland Security and Counterterrorism, said: “The president authorised action at this time because it was the national security team’s assessment that these hostages were in danger with each passing day in ISIL custody.

“The US government had what we believed was sufficient intelligence, and when the opportunity presented itself, the president authorised the Department of Defence to move aggressively to recover our citizens.”

She added: “Their effort should serve as another signal to those who would do us harm that the United States will not tolerate the abduction of our people, and will spare no effort to secure the safety of our citizens and to hold their captors accountable.”

It is not known how many foreign hostages are being held by IS fighters in Syria and Iraq.

Watch: Parents of slain journalist Foley praise their 'fearless' son