Douglas McCain was reportedly killed in a battle in Syria. Photo: BBC
An American man, believed to be fighting alongside Islamist militants in Syria, has been killed, the White House has confirmed.
A cousin of Douglas McCain told the BBC the US government called his mother to confirm his death on Monday.
McCain was found dead by Free Syrian Army fighters after a battle at the weekend, according to NBC.
The US government believes a small number of Americans have travelled to Syria to fight for extremist groups.
Senior US officials told broadcaster CNN McCain was fighting for Islamic State (IS), which now controls large areas of Iraq and Syria.
"My family is accepting the confirmation that was given to us by the government," his cousin Jocelyn Smith told the BBC. "I am really shocked."
Smith said the family had not been surprised when McCain converted to Islam a decade ago, but had no idea he had travelled to Syria or was potentially fighting for militants there.
"He was a beautiful person and whatever thoughts that were going on that made him make this decision were not out of hate," she said.
"I thought he was in Turkey and why he was in Turkey was unclear to us."
McCain was born in the US state of Minnesota and had moved to California with family, she added.
Western officials have warned of foreign fighters returning to the US and Europe after receiving training in Syria.
"We were aware of US 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."
Pentagon spokesman Rear Adm John Kirby told the BBC's Katty Kay the death "brings home one of the real threats here about [IS] and why we think about them in an imminent way".
The US ordered air strikes against IS in Iraq and Mr Obama has called the militant group a "cancer".
After the killing of journalist James Foley by the group, they are demanding more than $6m (£3.6m) for the ransom of a female foreign aid worker, US media report.
The 26-year old woman was working for a number of humanitarian organisations in Syria when she was kidnapped last year.
The US government and the woman's family have requested she not be named because of fears for her safety.
The woman is one of at least three known hostages currently held by IS militants.
Another is the US journalist, Steven Sotloff, who was seen alive at the end of the footage that showed James Foley's execution.
The militants have also demanded the release of the Pakistani neuroscientist, Dr Aafia Siddiqui, who is being held in a Texan jail after she was convicted in 2010 of planning to attack US officials.