American fighting for Islamic State killed in Syria

“We were aware of U.S. citizen Douglas McAuthur McCain’s presence in Syria and can confirm his death," National Security Council spokeswoman Caitlin Hayden said in a statement. "We continue to use every tool we possess to disrupt and dissuade individuals from traveling abroad for violent jihad and to track and engage those who return."

McCain is believed to have traveled to Turkey, passing through Istanbul according to the testimony of several NBC sources, and then sneaking into Syria. His once tame social media presence indicated a trajectory of radicalization in recent years, posting the black flag of the Islamic State and other propaganda photos to Facebook this year.

Dozens of Westerners are believed to be fighting for the Islamic State and other extremist factions in Syria, prompting fears that radicalized veterans of the war there could return to target their home countries. Those concerns are even sharper in Europe, which has seen several deadly attacks by returned extremist fighters in recent years.

In July, Florida native Money Mohammed Abusalha blew himself up in Syria after burning his U.S. passport on camera. Abusalha was trained by the Nusra Front, which is Al-Qaeda’s official branch in Syria and was once united with the Islamic State.

Also Tuesday, a family representative announced that a 26-year-old American woman was being held by the Islamic State, making her the third American known to have been kidnapped by the group. The woman was in Syria doing humanitarian aid work when she was taken hostage, but the representative did not say when she went missing.

The family representative and U.S. officials have asked that the woman not be identified out of fear for her safety. All spoke on condition of anonymity because they were not authorized to discuss the issue publicly.

On Wednesday, journalist Peter Theo Curtis returned home to the United States on Tuesday, two days after being freed by a Syrian extremist group that held him hostage for 22 months, his family said.

"I have been so touched and moved, beyond all words, by the people who have come up to me today — strangers on the airplane, the flight attendants, and most of all my family — to say welcome home," Curtis said in the statement.

Earlier this month, freelance journalist James Foley of Rochester, New Hampshire, was beheaded by the Islamic State, which kidnapped him in November 2012. Foley, 40, was in northern Syria on assignment for Agence France-Press and the Boston-based media company GlobalPost when he was captured.

The Islamic State released a video of Foley's beheading that also showed another missing American journalist, Steven Sotloff, and warned he would be killed next if U.S. airstrikes on Islamic State targets in Iraq continued. U.S. officials believe the video was made days before its release and have grown increasingly worried about Sotloff's fate.

Al Jazeera and wire services