US journalist Peter Theo Curtis is shown in this undated still frame taken from video courtesy of Al Jazeera, on Aug 2, 2014. [Photo/Agencies]

WASHINGTON - An American journalist kidnapped and held hostage for nearly two years by an al-Qaida-linked group in Syria was released Sunday, less than a week after the horrific execution of American journalist James Foley by Islamic militants.

The freed American is 45-year-old Peter Theo Curtis, who wrote under the byline Theo Padnos.

White House national security adviser Susan Rice said Curtis is now safe outside of Syria. Secretary of State John Kerry said Curtis was held by Jabhat al-Nusra, also known as the Nusra Front, an al-Qaida-linked militant group fighting the government of Syrian President Bashar Assad.

Curtis was not believed to be among the hostages held by the Islamic State group that executed Foley. Islamic State was formally disavowed by al-Qaida earlier this year after being deemed too brutal.

US President Barack Obama, who was wrapping up a vacation in Massachusetts, was briefed Sunday morning on Curtis' release.

"The president shares in the joy and relief that we all feel now that Theo is out of Syria and safe," said White House spokesman Eric Schultz. "But we continue to hold in our thoughts and prayers the Americans who remain in captivity in Syria, and we will continue to use all of the tools at our disposal to see that the remaining American hostages are freed."

A senior administration official said Curtis was released in the Golan Heights, where he was met by US government personnel who were transporting him to Tel Aviv. The official was not authorized to speak by name and discussed the release on the condition of anonymity.

Qatar's Foreign Ministry confirmed late Sunday that the Gulf emirate succeeded in gaining Curtis' release. A government statement released by the official Qatar News Agency said he was kidnapped in Syria in 2012 and said Qatar "exerted relentless efforts to release the American journalist out of Qatar's belief in the principles of humanity and out of concern for the lives of individuals and their right to freedom and dignity." The agency said Curtis was handed over to United Nations representatives.

In a video obtained by The Associated Press and dated July 18, 2014, Curtis sits cross-legged on a floor with his hands bound, and appears to read from a sheet placed in front of him on the floor. Addressing the US and European governments, he pleads for them to contact a named intermediary before it is too late.

"They have given me three days to live," he says as a man holding an assault rifle and dressed in camouflage stands next to him. "If you don't do anything, I'm finished. I'm dead. They will kill me. Three days. You have had 20 days, and you've done nothing. "

He does not specify any demands, only urges Western governments to make contact with the intermediary.

It was not known which, if any, of the captors' demands were met.

The energy-rich Gulf nation of Qatar, which is a leading supporter of the Syrian rebels fighting to oust President Bashar Assad, has been involved in mediating hostage releases in Syria over the past year.

In March, the Qataris helped negotiate the release of more than a dozen Greek Orthodox nuns held by the Nusra Front. Late last year, Qatar also helped broker a deal that saw nine Lebanese pilgrims held in Syria by rebels go free in exchange for the release of two Turkish pilots held hostage in Lebanon.