The father of two young British Muslims killed while fighting in Syria has said his grief "cannot be described" as he claimed the Government was "criminalising" young Britons who have travelled to the war-torn country.
Abubaker Deghayes said his 17-year-old son Jaffar was shot in the head by President Bashar al-Assad's forces near the city of Aleppo.
The teenager, who is believed to have died at the weekend, left his home near Brighton earlier this year in a bid to overthrow the Syrian dictator.
His brother, Abdullah, 18, was killed in Latakia province in April after leaving the UK in January to reportedly take up arms with Jabhat al-Nusra, an al-Qaida-affiliated group.
Yesterday the pair's brother, Amer, 20, who also travelled to Syria, relayed news of the death of Jaffar to their father who lives in Saltdean, East Sussex.
Speaking outside his home tonight, Mr Deghayes, said he felt "great sadness, sorrow and pain" following the deaths of his two sons.
In footage shown on Sky News, he said: "The grief for my sons Jaffar and Abdullah cannot be described. My words fail to describe it.
"I cried my eyes yesterday and I really hope and pray to God that Amer is safe and returns home safe to his homeland, Brighton, where he lived all his life.
"My message is still the same - all young Muslims...who think to go to Syria out of kindness, out of trying to make a difference, do not go. The Syrians do not need foot fighters.
"They need weapons, they need governments to help them, they need quality weapons to fight the aircrafts of Assad. You can help from here. Do not make this mistake.
"Please don't let you're families go through what we are going through."
In a direct message to Prime Minister David Cameron and Home Secretary Theresa May, Mr Deghayes said: "You have stopped me from trying to go there to bring my sons back by keeping my passports for five or six months.
"If I wanted to join the fight in Syria, I could have done that. I have been to that country five or six times and stayed there carrying out aid work.
"The strategy you are using with our sons does not work. You are criminalising them just out of the fear they might become a threat to this country.
"Do not push them to be radicalised, used by groups like Isis who are out for revenge and thirst for blood.
"You should have a strategy where we teach youngsters here in this country to work in relief work and to know and to experience how to help in a civilised manner.
"And also have an exit strategy for those who went there. They can't come back without the fear of their own people, their own government.
"They should be treated like youngsters who made a mistake and it should be dealt with like that, not just sent to prison. The stick of the law does not work all the time.
"Mr Cameron, please revise your strategy and the Government's strategy at this point. It's very vital, it's very important. We do not want to lose more youngsters."
Mr Deghayes said Jaffar had died 15 minutes after being shot while part of a group of five "special force fighters".
The Deghayes brothers are the nephew of Omar Deghayes, who was held by the United States as an enemy combatant at Guantanamo Bay detention camp between 2002 and 2007 after he was arrested in Pakistan.
Following the death of Abdullah earlier this year, counter-terrorism officers raided the Deghayes' family home in May and seized material after a warrant was issued under the Terrorism Act 2000.
In a film shot by Vice News this year, Amer Deghayes said he had no intention of returning to Britain, adding: "My work here is not done.
"I came here to give victory to the people and make sure that they receive justice, and we still haven't reached the goal yet."
Counter-terrorism investigators have expressed concern about aspiring British jihadis travelling to Syria and becoming radicalised.
It emerged this month that a fourth man from Portsmouth, Hampshire - 19-year-old Muhammad Mehdi Hassan - died fighting in Kobani.
Three others from the same city - Iftekar Jaman, 23, Mamunur Roshid, 24, and Muhammad Hamidur Rahman, 25 - have also been killed after travelling there in October last year.
In January alone, 16 people were arrested on suspicion of terrorism offences related to Syria compared with 24 arrests in the whole of last year.
Others who have died include one man suspected of carrying out a suicide attack.
Abdul Waheed Majeed, 41, is believed to have driven a lorry to a jail in Aleppo before detonating a bomb in February.
The married father-of-three, who was born and raised in Crawley, West Sussex, left Britain in 2013, telling his family he was going on a humanitarian mission to Syria.
Sussex Police has urged anyone who has concerns or information about anyone locally planning to travel to Syria or Iraq to contact the force.
A police statement said: "The south east counter-terrorism unit (Sectu) and Sussex Police are aware of recent social media postings reporting the death of a man who may have come from Brighton during fighting in either Syria or Iraq.
"Whilst we will not comment on individual cases, reports like these remind everyone that the situation in Syria and Iraq is unsafe and that risk of injury, death or abduction remains for anyone travelling to that area.
"The Government advice continues to be that no one should travel to these war zones and that the most effective way to help the affected population is through humanitarian support."
A Foreign Office spokesman said: "We are aware of reports of the death of a British national in Syria.
'The UK has advised for some time against all travel to Syria, where all UK consular services are suspended.
"As we do not have any representation in Syria, it is extremely difficult to get any confirmation of deaths or injuries and our options for supporting British nationals there are extremely limited."