An American man suspected of fighting alongside Islamic State militants who have seized large areas of Iraq and Syria to the alarm of the Baghdad government and its allies in the West has been killed in Syria, a U.S. official said Tuesday.

"We were aware of U.S. Citizen Douglas McAuthur McCain's presence in Syria and can confirm his death," U.S. 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," Hayden said.