A video posted online Tuesday appears to show the beheading by Islamic militants of U.S. journalist James Wright Foley, who was kidnapped in November 2012 while covering the civil war in Syria.

The video, whose authenticity remains to be determined, shows Foley, 39, kneeling before his hooded executioner at an unspecified desert location.

Purporting to be the work of the Islamic State group, which has proclaimed a caliphate in parts of Syria and neighboring Iraq, the video includes footage of President Barack Obama's announcement authorizing U.S. airstrikes against IS in northern Iraq.

"I call on my friends, family members and loved ones to rise up against my real killers, the U.S. government," Foley says to the camera. "For what will happen to me is only a result of their complacency and criminality."

"I call on my brother John, who is member of the U.S. Air Force, think about what you are doing, think about lives you destroy including those of your own family," the journalist continued.

"I died that day John, when your colleagues dropped that bomb on those people - they signed my death certificate," Foley said.

Foley, who spent time in a Libyan jail in 2011 while covering the revolution that ultimately toppled Moammar Gadhafi, was reporting from Syria for the U.S.-based GlobalPost at the time of his abduction.

"I wish I had more time, I wish I could have the hope of freedom and see my family once again, but that ship has sailed. I guess all in all, I wish I wasn't American," Foley concluded.

Speaking in English, the black-clad executioner warns that Obama's authorization of airstrikes against IS places the United States "upon a slippery slope towards a new war front against Muslims."

"Any attempt by you, Obama, to deny Muslims liberty and safety under the Islamic caliphate, will result in the bloodshed of your people," the militant added before decapitating Foley, whose severed head appears over his lifeless body.

Following the apparent execution, an ISIS fighter appears standing next to another U.S. journalist who was kidnapped in Syria, Steven Joel Sotloff

"The life of this American citizen, Obama, depends on your next decision," the fighter says. EFE