A jihadist fighter with the al-Qaeda-linked Jabhat al-Nusra group is thought to have become the first Briton to carry out a suicide attack in Syria.
The man, known only by his nom de guerre, Abu Suleiman al-Britani, was said to have blown himself up during a raid on a prison in Aleppo.
He had driven a truck packed with explosives into Aleppo's central jail yesterday, according to British fighters in Syria. Hundreds of rebels followed behind, managing to free up to 300 prisoners held by Syrian forces.
If confirmed, Britani - believed to be British-born and of Pakistani origin - would be the eighth Briton to die fighting since Syria's bloody civil war began three years ago.
A photograph taken before the attack which was posted on Twitter appears to show Britani inside a modified truck, or Vehicle Borne Improvised Explosive Device (VBIED), which is decked with the black Jabhat al-Nusra flag.
Another picture shows large plumes of spoke rising from the site after the device was detonated. Charles Lister, a terrorism adviser at the Brookings Center in Doha, Qatar, told the Telegraph he was "99 per cent" sure that Britani was killed in yesterday's suicide truck attack.
Shiraz Maher, a senior research fellow at the International Centre for the Study of Radicalisation at Kings College in London, made contact with British citizens known to be in Syria in order to confirm the reports. In a text reply, he was told: "Lol, yes, news travels fast. The first British brother!"
A fellow fighter, using the name Abu Yehya Al-Sham, wrote on Twitter: "So a brit done the martyerdom op to free the prisoners of Halab (Aleppo), a sacrifice that is heroic in the eyes of many n villainous in others..." Another, Abu Fulan al-Muhajir, wrote: "May allah accept him.
All british muslims should be proud of him. I am, and I'm not even British. "I met brother Abu Sulayman al-Britani. He looked so beautiful dressed all in white, standing on top of the car shouting "takbeer" (Allah is great)."
There are thought to be several hundred Britons fighting in Syria's civil war. Earlier this week a jihadist from Islamic State in Iraq (ISIS), a rival Islamist group, was killed during fighting against rebel groups at the border town of al-Rai.
A "war within a war" has burgeoned in Syria in recent weeks, with local rebels seeking to destroy ISIS, which is dominated by foreign jihadists. One of the last Britons to die in a suicide attack was in Gaza in 2003.
Asif Mohammed Hanif, 21, a British citizen of Pakistani origin, killed three people when he blew himself up in a pub in Tel Aviv. In 2007, a 21-year-old British student reportedly committed a suicide attack at a military checkpoint killing up to 20 soldiers in the southern Somali town of Baidoa.
By Josie Ensor, and Ruth Sherlock