Kidnappers in Syria have freed a U.S. journalist missing since 2012, U.S. Secretary of State John Kerry said on Sunday, following what Qatari-owned Al Jazeera said were efforts by the Gulf Arab state to win his release.

Kerry said in a statement announcing the release of Theo Curtis that the United States was using ¡°every diplomatic, intelligence and military tool¡± at its disposal to secure the release of other Americans held hostage in Syria.

News of Curtis¡¯s release emerged just days after Islamic State militants this week killed American journalist James Foley, who was kidnapped in Syria in 2012.

A Qatari source told Reuters Curtis had been handed over to a representative of the United Nations in Syria. ¡°Qatari intelligence agencies were behind the release of the American journalist in Syria. Qatar, like many countries, looks to free those in captive for humanitarian reasons,¡± the source added.

The Qatari source did not have details on what Qatar had done to free him, saying only that it had been a matter of ¡°communication with the right people in Syria.¡±

The release happened just days after the Islamic State militant group fighting in Iraq and Syria issued a video showing Foley¡¯s beheading.

That video, together with a threat to kill another American journalist being held hostage, Steven Sotloff, inspired widespread revulsion in the West and a desire to hunt down the killer.

The Qatari source said he did not know if Qatar was involved in seeking to free other journalists, but added that ¡°any captives with (Islamic State) will be very difficult for Qatar to free, while others with different groups would be easier.¡±

The U.S.-based Committee to Protect Journalists estimates that about 20 journalists are missing in Syria. Many of them are believed to be held by Islamic State.

In a video statement released by Curtis¡¯s kidnappers at some point during his captivity, Curtis said he was a journalist from Boston, Massachusetts, Al Jazeera reported. Commenting on his treatment in that video, Curtis said he ¡°had everything¡± he needed and ¡°everything has been perfect, food, clothing, even friends now.¡±