London (CNN) -- Foreign fighters inside Syria and Iraq have become a massive concern for authorities worldwide. Many are alarmed at the quick rise in the number of Westerners who have joined militant groups trying to establish an Islamic caliphate, with several investigations launched following the gruesome beheading of American journalist James Foley last week.
We have been tracking foreign fighters going into Syria for more than a year. During this time, we came across two young men willing to speak to us through Skype from inside the country, where they are helping battle President Bashar al-Assad's forces. We first spoke to them couple of months ago and have been in touch since.
After much back and forth -- and a lot of convincing -- they agreed to an interview with us from northern Syria, using Skype in what looked like a hidden internet cafe. As expected, the connection was not great and it took several attempts to finally talk to them.
Despite having spoken to the pair before, it was not easy to identify which masked militant was which. As they sat down to begin the interview they were careful to adjust their scarves to cover most of their faces. An AK-47 was positioned deliberately and carefully between them. With unintended humour and in a serious fashion they reintroduced themselves by their jihadi aliases: Abu Bakr and Abu Anwar.
Abu Bakr was open to talking with us and he gradually agreed to bring other fighters along for an on-camera interview, a process made tougher as both Bakr and Anwar change locations every couple of months.
Abu Bakr wouldn't tell us where he is from but Abu Anwar is British. "I'm from the south of England," he explained. "I grew up in a middle-class family. Life was easy back home. I had a life. I had a car. But the thing is: you cannot practice Islam back home.
"We see all around us evil. We see paedophiles. We see homosexuality. We see crime. We see rape. And we can't do anything about it because we are obeying [by] the laws of the kuffar."
Initially, both fighters came to Syria to join the rebel alliance against the regime of Bashar al Assad -- but they now believe that establishing an Islamic caliphate is more important.
When we asked Abu Anwar what message he had for friends back home, it was a call to join the fight.
"Leave the lands of infidelity and leave for the lands of Islam," he said. "We have an Islamic state in Raqqa. Alhamdulillah ["All praise and thanks to God"] now in Iraq. And I ask all my Muslim friends to make hijrah ["holy journey"] to these Islamic states."
In all our conversations, both men proved unfailingly polite. They patiently answered our questions, determined for us to see their point of view: for them, America is an immoral country at war with Muslims
Our talk was dominated by discussions of what they see as American injustices, from Guantanamo to Abu Ghraib. They also called for the release of Aafia Siddique, a female U.S. trained scientist convicted in 2010 of shooting at U.S. officers while in custody in Afghanistan. Abu Bakr became agitated as he mentioned he has heard word that there are other Muslim female prisoners, held in American custody, who are given the same treatment as men. Both Bakr and Anwar agreed that this was a complete injustice.
In our most recent interview we asked them about the videotaped killing of American journalist James Foley.
"When the video was released we watched it in our base and one of the brothers downloaded it and my initial response was that this was a direct response to the crimes of the US against the Islamic State," said Abu Anwar.
Abu Bakar added: "We thought the Islamic state has no other choice really. The U.S. has the technology but it doesn't mean they can call any country and bomb anybody they want and not stop on anything. ISIS tried to negotiate for a Muslim prisoner, tried to negotiate with them for ransom but then they are too arrogant you see. We thought it was very justified and we thought what James Foley said himself... that his real killers were actually the U.S."
Their interpretation of Islam is radical and extreme: their sense of justice is medieval and they call the Muslim Council of Britain, the UK's largest Muslim organization, "apostates." We asked them if they would consider carrying out an execution by beheading.
"This is the Islamic way of execution and we will do only that which please Allah," replied Abu Anwar. "It means cutting off the necks of the enemies of Islam then we are more than happy to do it. I would like to meet the Lord Allah and tell him what I did for his religion. I hope God gives me the chance to do what the brother did with James Foley. Whether it's James Foley, or a soldier of America or Bashar Al Assad... my hands are ready to do this blessed act."
But when we asked why they continue to support ISIS -- when even al Qaeda has condemned the group's brutality -- they initially struggled to answer and their commitment wavered.
"It's a tactical difference," explained Abu Bakr. "Basically al Qaeda doesn't say they are very brutal. They have operational differences with them. And they disagree with them. But whatever is Islamically allowed, we do it. It doesn't matter which group it is and what it is called, ISIS or al Qaeda."
We had asked for more details; on the battles they fought, on where they are positioned. But the men were cautious not to give too much away. They have sent us pictures of their basic training in a militant camp: in one photo, Abu Bakr is positioned in a foxhole holding a Kalashnikov.
The only time they seemed to pause in their Islamist rhetoric was when discussing their families. When we first asked Abu Anwar what his mother would say, he was silent, refusing to talk about them.
It's clear that both expect to die in Syria, either in battle or in what they call a "martyrdom mission," a suicide attack against enemy forces. Abu Anwar said that his family has given up hope of trying to bring him back.
"No. They don't ask me to come back any more. Because they did at the beginning but they know now that I am not coming back. So, there is no point in wasting their breath. We pray a lot that Allah give you success and Allah accepts this jihad from you. They understand that I am not coming back and they know that they will not see me again in this life."