Three westerners including an American and a Briton are reported to have been killed in a government ambush in the Syrian town of Idlib, according to a foreign-based human rights group.
The family of Nicole Mansfield, a convert to Islam from the US state of Michigan, say the FBI has confirmed her death.
The British man is said to have been a 23-year-old Londoner, but the Foreign Office in London said it could not confirm any details about him, though his name was reported by Syrian TV.
A Foreign Office spokesperson said: “We are aware of the claims. We have no verification, but are seeking information.The UK has warned for some time against all travel to Syria.”
The third person has not been identified.
The reports are unconfirmed but the westerners were said to have been with rebel forces when they were attacked by the Syrian army.
The Syrian government’s official news agency, SANA, said Mansfield and two other rebels were confronted by Syrian soldiers. The report said Mansfield and the others threw hand grenades at the soldiers before being shot and killed.
Syria’s state-run TV broadcast pictures of her passport and driving licence.
The rights group, the UK-based Syrian Observatory for Human Rights, has also said the government controls most of Qusair following a fierce 12-day battle.
Syrian rebels have pleaded for military and medical aid in the town.
The Lebanese militant group Hezbollah has said it has joined the battle on the government’s side from across the border.
In the central province of Homs where Qusair is located, as well as in Damascus, rebels have suffered setbacks around their supply routes.
Unverified amateur footage said to be from the district of Maskana in Aleppo purports to show people using their bare hands to recover bodies following heavy shelling by government forces.
Mansfield’s aunt, Monica Mansfield Speelman, said she had not been told by the FBI how her niece had died.
Speelman added: “I’m just devastated. Evidently, she was fighting with opposition forces.”
In an interview with Reuters, Speelman said Mansfield, a 33-year-old single mother of an 18-year-old daughter, had converted to Islam about five years ago and had at one stage been married to an Arab man. She said she did not know when her niece had traveled to Syria.
“I didn’t think she would stoop that low to go over there and try to harm anybody,” Speelman said of her niece, who she said had previously worked as a healthcare assistant for the elderly and at a group home.
Her grandmother, Carole Mansfield, told the Associated Press: “She had a heart of gold” but was easily influenced by others. She added: “I think she could have been brainwashed.”