California-born Douglas McAuthur McCain has become the first American jihadi to have died in Syria while fighting for Islamic State of Iraq and Syria, a terrorist outfit that has gained control of large parts of Syria and Iraq.

The death of the 33-year-old American has left many top US officials seriously concerned. "We were aware of US Citizen Douglas McAuthur McCain's presence in Syria and can confirm his death. We continue to use every tool we possess to disrupt and dissuade individuals from travelling abroad for violent jihad and to track and engage those who return," Caitlin Hayden, spokesperson of the National Security Council, the White House said.

According to the Britain-based Syrian Observatory for Human Rights, McCain died in a battle between rival extremist groups in the suburbs of Aleppo, the commercial capital and largest city of Syria. His uncle, Ken McCain told the CNN that Douglas McCain converted from Christianity to Islam several years ago.

The fact that he became a jihadi left his family "devastated" and "just as surprised as the country," the uncle said.