19-year-old Mehdi Hassan, with British private school education, is the fourth Islamic State recruit from Portsmouth to be killed while fighting in Syria.
Hassan, who has his roots in Bangladesh, reportedly arrived in Syria earlier last year, along with a group which called itself the "Britani Brigade Bangladeshi Bad Boys".
ISIS-affiliated accounts announced the death of its 'martyr' on Twitter on Friday. Hassan's family learned of his death only late on Saturday, after reports of his death in Syria went viral on Twitter.
ISIS also posted a picture of Hassan's body, claiming that the 'brother' was killed during the fighting in Kobane.
— Official Ghazi (@ghazi_dimashqi) October 24, 2014
Kobane, located near Turkey, has been battling Islamic State insurgents for the last one month.
The US-led coalition's airstrikes have targeted ISIS locations around the Kurdish city. Reports claim that over 300 militants have been killed in Kobane.
A report in The Independent stated that the British Foreign Office could not confirm Hassan's death but stated that it "was aware of reports about the death of a British national in Syria".
"It has been confirmed with the family that he has died. Right now they are very upset," Abdul Jalil, the chairman of Portsmouth's Jami Mosque, told BBC after speaking to the relatives of Hassan.
"I am saddened and again shocked for the community about this news," he added.
Hassan, prior to joining the Islamic State, was a pupil at the private elite school St John's College in Southsea. However, reports indicate that somewhere around October 2013, he and his friends flew to Turkey and then crossed over to Syria to join ISIS.
The other youths killed in Syria before Hassan have been identified as Hamidur Rahman, Iftekar Jaman and Mamunur Roshid.
Hassan, who tweeted under the name Abu Dujana from Syria, made the last post on his Twitter account @AbuDujana on 17 October. He referred to the intense airstrikes in Ayn al-Arab, another name for Kobane, in that post.
"Between 20-40 us strikes daily in ayn al arab. Alhamdulillah they are spending $10's of billions... against themselves," he tweeted.
Reports indicate that while Hassan's death is being mourned in Portsmouth, among the thousands of ISIS fighters - including the over 500 from the US - he is being celebrated for achieving 'martyrdom'.