An engineering student who left his life in the U.K. to fight with Islamist extremists who have seized parts of Iraq and Syria has described his journey to join the militants as one of the happiest moments of his life. Abdul Raqib Amin was studying in Aberdeen, Scotland, but last month appeared in a recruitment video for the Islamic State of Iraq and al-Sham (ISIS) aimed at other Westerners. In an exclusive interview with NBC News’ U.K. partner ITV News aired Monday morning, the British citizen admitted he missed his parents but said that he “left the house with the intention not to go back.”

“I’m going to stay and fight until the Khilafah [rule of Islam] is established or I die,” he told Good Morning Britain. “One of the happiest moments of my life was when the plane took off from [London’s] Gatwick Airport. I was so happy, because as a Muslim, you cannot live in the country of Kuffars [disbelievers].” Experts warn the rapid advance of ISIS has created an online buzz that is “very attractive” to potential foreign fighters – and a national security headache for counter-terrorism officials around the world.