A US citizen suspected of fighting alongside Islamic State group fighters, who have seized large swathes of Iraq and Syria, has been killed in Syria, a US official has said.
The White House late on Tuesday confirmed the death of Douglas McAuthur McCain, 33 - a one-time aspiring rapper and basketball fan from California.
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McCain, who converted from Christianity to Islam about a decade ago, was killed in fighting against the al-Nusra Front, an al-Qaeda-linked group blacklisted by Washington, US media reports said.
"We were aware of US Citizen Douglas McAuthur McCain's presence in Syria and can confirm his death," US National Security Council spokeswoman Caitlin Hayden said in a statement.
"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."
A national security official who asked not to be named told the Reuters news agency that the FBI was investigating McCain's death, and a State Department spokeswoman said officials had been in contact with his family and were providing "all consular assistance".
The Minneapolis Star Tribune newspaper reported that the family had been concerned with McCain's expressions of support of Islamic State fighters.
McCain's death comes as the West has been alarmed by the participation of foreign fighters in Syria and Iraq, particularly from the US and Europe.
The US State Department estimates that there are about 12,000 foreign fighters from at least 50 countries in Syria.
US Attorney General Eric Holder said federal prosecutors had opened fewer than 100 investigations into citizens who may had travelled to Syria or Iraq to fight.
In May, a 22-year-old man from Florida carried out a suicide bombing in Syria's Idlib province, while a Denver woman was arrested in July on suspicion of trying to fly to Syria to support fighters.
Meanwhile, US President Barack Obama vowed "justice will be done" against the Islamic State killers of American journalist James Foley on Tuesday as the US began surveillance flights in Syria.
Obama's comments followed his decision to approve aircraft and drone surveillance to gather intelligence on Islamic State sites in Syria.
But American officials have said they did not plan to coordinate with Damascus on targeting fighters in Syria, despite Syrian insistence that any military action on its soil must be discussed in advance.
"There are no plans to coordinate with the Assad regime as we consider this terror threat," White House spokesman Josh Earnest said in Washington on Tuesday.
The US has already been conducting airstrikes on positions held by the Islamic State group in neighbouring Iraq.