An American woman identified as Nicole Mansfield is reportedly among three Westerners killed in Syria's Idlib province.
The 33-year-old woman from Flint, Mich., died fighting government forces, according to Syria's state-run news agency SANA.
The US government has not confirmed that Mansfield was killed, but her mother and cousin told the Detroit Free Press that the FBI broke the news to them on Thursday afternoon.
The site described Mansfield as an extremist who joined local rebels alongside two people from the UK, one of whom appears to be a 22-year-old man from London.
Mansfield's family described her as a good-natured woman who may have been misled.
"I'm sick over it," her aunt, Monica Mansfield Speelman, told the Detroit Free Press. "I didn't think she was [a terrorist], but God only knows."
Mansfield Speelman did not know how long her niece had been in Syria before her death, she told Reuters. "I didn't think she would stoop that low to go over there and try to harm anybody," she said. "I'm just devastated. Evidently, she was fighting with opposition forces."
According to her relatives, Mansfield married an Arab man whom she later divorced, converted to Islam, and around two or three years ago moved to Dubai. She leaves behind an 18-year-old daughter.
Pro-Syrian government news site Breaking News Sy posted graphic photos of a body it claimed was Mansfield's, along with photos of her US passport.
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Syrian media reported that Mansfield was setting up an observation post in rebel-controlled Idlib province and threw hand grenades at a group of Syrian soldiers before being shot and killed.
The UK-based Syrian Observatory for Human Rights said that one of the three Westerners killed was a man with a British passport identifying him as being from London, the BBC reported.
The British Foreign Office confirmed that the man was a British national and added that his family had been informed.
A spokeswoman said, "We understand a British national has been killed in Syria. Their family has been informed and we are providing consular assistance," according to the BBC.
A Syrian state TV report named the man, showed what the report alleged was his passport, and said he was born in 1990, according to the Times. It showed three bodies lying next to a bullet-riddled car.
The three were photographing military positions near the Turkish border, SOHR director Rami Abdel Rahman told the Times.
"They were shot dead during an ambush in the Idlib region and the army found them with maps of military positions," Rahman said.
The BBC said the unidentified British national's death was thought to have happened Wednesday, the same day that British doctor Isa Abdur Rahman was also killed in the region.
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Meanwhile, in Syria, more than 1,000 rebel fighters have reportedly entered Qusayr to augment the opposition forces fighting the Assad regime's troops. Abdul-Rahman of the Observatory said hundreds of rebel fighters broke through army lines northeast of the beleaguered city.
Syrian President Bashar al-Assad's troops have also been receiving foreign support, from the Lebanese Shia militant group Hezbollah, as the conflict threatens to spill over borders.
The battle in Qusayr, which has been raging since May 19, is over securing supply routes near the border of Syria and Lebanon.
Later on Friday, activists said government troops attacked a medical convoy in Qusayr, killing roughly seven and injuring dozens.
The attack happened near the Lebanese border, The Associated Press said.
"Women and children jumped out of the cars and started running in fear," activist Hadi Abdullah told the AP via Skype.
Abdullah said roughly 800 wounded remain trapped in Qusayr, and healing them would be more difficult after loyalist troops attacked a home converted into medical clinic and a hospital.
GlobalPost senior correspondent Corinne Purtill contributed to this report from London.