Security services believe that around 100 British nationals may have been killed waging jihad in Syria and Iraq since the start of the Syrian civil war.

Worryingly it is thought that up to 50 'high risk' jihadists may have returned to the UK after gaining jihadi training and combat experience whilst fighting in Syria and Iraq.

Concerns remain that the returnees may be planning to carry out terror attacks in the UK and could be operating as a cell, similar to the perpetrators of the Paris attacks in November 2016.

Mohammed Emwazi, also known as jihadi john, was killed in an airstrike in November 2015

Former Holland Park school pupils Nassim Terreri (left) , 25, and Mohammed al-Araj (right) were both killed in Syria. University of Hertfordshire student Ibrahim al-Mazwagi (centre), 21, became the first confirmed British jihadi to be killed fighting in Syria when he was shot in February 2013

British Moroccan Choukri Ellekhlifi (left), 22, from West London, who attended the same school as Jihadi John, was killed in August 2013 while fighting for Jabhat Nusra. North London brothers Akram Sebah (right), a 24-year-old estate agent, and former English foreign language teacher Mohammed Sebah (centre), 28, were killed in Syria in September 2013

'There's been a lot of British people killed out there - up to 100 now and there's every chance that that number will continue to grow,' a security source told The Sunday Times.

High profile British fighters including Mohammed Emwazi and Junaid Hussain have been killed in recent months following the coalition's increasing use of drone strikes to target individual fighters.

Reyaad Khan, a British ISIS fighter originally from Cardiff, was the first British national to be killed by an RAF drone when his vehicle was hit in Syria.

The Welsh jihadi had appeared in a 14-minute propaganda video in June 2014, urging people to join ISIS and threatening attacks on the West.

Reyaad Khan, originally from Cardiff, came to prominence after appearing in a ISIS propaganda video

Former call centre worker Ifthekar Jaman (left), was one of the first Britons to join ISIS and encouraged others to fight with him in Syria. He was killed in December 2013. Anil Khalil Raoufi (centre), studied in Liverpool and was originally from Manchester. Crawley bomber Abdul Waheed Majeed (right) was filmed driving a lorry full of explosives into the walls of Aleppo prison in February 2014

Abdullah Deghayes (left), 18, and his brother Jaffar (centre), 17, from Brighton, died fighting for Jabhat Nusra. Former Holland Park school student Mohammed Nasser (right), 21 was killed by shrapnel in 2014

Abdul Rakib Amin (left), from Aberdeen, appeared in an ISIS propaganda video alongside two British fighters from Cardiff. Former Primark supervisor Muhammad Hamidur Rahman (centre), 25, from Portsmouth was killed in Syria. Ibrahim Kamara (right), 19, from Brighton was killed fighting for Jabhat Nusra

Madhi Hassan (left), 20, from Portsmouth, an avid body builder, was going to start a degree at Surrey University before he travelled to Syria and died in October 2014. Abu Abdullah al-Habashi (centre), 21, from London, converted from Christianity and appeared in a jihadi propaganda video, was killed in Kobani, Syria. Abu Hajar al-Britani (right) carried out a deadly suicide bomb mission in the oil-rich Iraq town of Baiji.

Computer hacker Junaid Hussain was killed in a drone strike last year in Raqqa

Last week fresh statistics revealed that as many as 60 girls and women have left to UK to live in Syria and Iraq under ISIS's radical interpretation of Shariah law.

Intelligence sources also believe around 100 British children are thought to be living in ISIS-held territory, according to The Sunday Times.

Schoolgirls as young as 15 have joined ISIS, where they are expected to marry a fighter and live in the deadly warzone.

There have also been reported cases of whole families, including elderly grandparents, travelling to Turkey and being smuggled into the warzone.

ISIS have recently suffered setbacks in Iraq, where it is believed they have lost as much as 40 per cent of their territory.

The group have tightened up their media coverage and implemented a ruthless campaign in a bid to hunt down 'spies' giving away information to Western security services.

Convicted criminal Kabir Ahmed (left) left his home in Derby and carried out a suicide mission in Iraq. Abu Malik as-Somali (centre) is believed to be from West London and died in January. Little is known about Londoner Abu Abdullah al-Britani (right) despite starring in numerous Rayat al Tawheed videos

Abu Musa as-Somali (left) is believed to have died in Kirkuk in Iraq. Ali Kalanter (centre) and Rashid Amani (right) were from Coventry and both died fighting in Kobani

Abu Dharda as-Somali (left), 20, from London, was a keen nasheed singer and died fighting for ISIS in late 2014. Luton bad boy Abu Rahim Aziz (centre) died last year in an airstrike in Raqqa, Syria. Abu Mohammed Al-Britani (right) also known as Oogali, was fighting for a Uzbek and Chechen battalion

Abu Hafs al-Pakistani (left) was a trainer for a splinter rebel group in Syria. Cardiff born Reyaad Khan (centre), 21, appeared in an ISIS propaganda video urging Muslims to join the jihadi group. Abu Muslim al-Muhajir (right) is believed to have fought for Rayat al Tawheed

Abu Abdullah al-Britani (left) was videoed carrying out a suicide attack. Suspected Rayat al Tawheed fighter Abu Tauba al-Muhajir (centre) is believed to have died in an explosion while working in an ammunition factory in Raqqa, Syria. Fatlum Shakalu (right) and is brother Flamur were originally from London and travelled to Syria in 2013. Fatlum carried out a huge suicide bomb operation in Ramadi, Iraq

Talha Asmal (left), originally from Manchester, is thought to be the youngest British suicide bomber and died last year. British Sudanese ISIS fighter Osman Mustafa Fagiri (centre) died in Syria, having previously fought in Mali. He was a former Pharmacy student at a private university in Sudan. Assad Uzzaman (right) was one of five men from Portsmouth in Hampshire who styled themselves the 'Britani Brigade Bangladeshi Bad Boys' and travelled to fight with ISIS in October 2013

Teenager Rohan Malik, (left) originally from Yorkshire, was killed fighting for ISIS. Little is known about British fighter Abu Khalid al-Britani (right)

Abu Basir al-Britani, is believed to have studied law and sociology in London. He was killed fighting near Latakia