The Foreign Office did not provide further details or identify the British national, but he was named in media reports as 22-year-old Londoner Ali al-Manasfi.
Britain's ITV television said Manasfi had disappeared from his home four months ago and his family had reported him missing to the police.
They later learned he had gone to Syria and he called his family from there several times.
Relatives were shocked to discover he had travelled to the conflict-torn country, describing him as a "big kid at heart", ITV said.
The Syrian Observatory for Human Rights had said on Thursday that three westerners including a US woman and a British man, both Muslims, had been killed in northwest Idlib province near the Turkish border.
The three had apparently been taking photos of military positions on the road between Harim and the town of Idlib further south when government troops ambushed them Wednesday, said Rami Abdel Rahman, director of the monitoring group.
The American woman is believed to be Nicole Lynn Mansfield, a 33-year-old Muslim convert from Flint in Michigan.
Her family were awaiting confirmation Friday that she was among the dead.
The nationality of the third Westerner was not clear, the Observatory said.
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Britain's ITV television said Manasfi had disappeared from his home four months ago and his family had reported him missing to the police.
They later learned he had gone to Syria and he called his family from there several times.
Relatives were shocked to discover he had travelled to the conflict-torn country, describing him as a "big kid at heart", ITV said.
The Syrian Observatory for Human Rights had said on Thursday that three westerners including a US woman and a British man, both Muslims, had been killed in northwest Idlib province near the Turkish border.
The three had apparently been taking photos of military positions on the road between Harim and the town of Idlib further south when government troops ambushed them Wednesday, said Rami Abdel Rahman, director of the monitoring group.
The American woman is believed to be Nicole Lynn Mansfield, a 33-year-old Muslim convert from Flint in Michigan.
Her family were awaiting confirmation Friday that she was among the dead.
The nationality of the third Westerner was not clear, the Observatory said.
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