An American man fighting for the Islamic State died in Syria, officials confirmed Tuesday.

Douglas McCain, a 33-year-old native of California, went to Syria to fight with the IS and join their cause of establishing an Islamic Caliphate.  Authorities said he died last weekend.

The first to report the death of McCain was NBC News. It reported that an activist connected with the moderate Free Syrian Army informed them about McCain's death. The person also provided NBC with photos supposedly of McCain's passport and body.

The news of McCain's death was, however, confirmed by the White House National Security Council Tuesday. "We were aware of U.S. Citizen Douglas McAuthur McCain's presence in Syria and can confirm his death," Caitlin Hayden, a National Security Council spokeswoman, said in an e-mailed statement, reports Bloomberg. "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."

One of McCain's relatives said the family was "devastated" and "just as surprised as the country" to find out that he was fighting with the IS. McCain was raised a Christian and converted to Islam several years ago, his cousin Ken McCain said, reports CNN.

"I know that he had strong Muslim beliefs," McCain's cousin said, reports the Star Tribune, "but I didn't know that he was in support of ISIS. I didn't think he would be." Another cousin noticed McCain's increasingly pro-IS Facebook posts and reached out to McCain on the social media site, asking, "'Where are you?'," explaining, "I just had a funny feeling."

In April McCain went to Turkey, where his family believed he stayed. On June 9, McCain tweeted to a possible IS militant, "I will be joining you guys soon." Later he tweeted again saying, "I'm with the brothers now."

Officials expressed concerns about such jihadi believers returning to the U.S. to commit terrorist acts, reports NBC.

There has been a surge in foreign fighters travelling to Syria in recent years. Two of them, Nicole Lynn Mansfield, a Muslim convert, 33, and Moner Mohammad Abu-Salha, 22 have died in the conflict, reports BBC.