Watch: Parents of IS converts regret not teaching 'modern Islamic values' to children

According to one independent Western estimate, between 16,000 and 17,000 men and a small number of women from 90 countries or more have streamed to Syria and Iraq to wage Muslim holy war for the Islamic State. The contingent of foreigners who have taken up arms on behalf of Islamic State during the past 3 1/2 years is more than twice as big as the French Foreign Legion. An anguished father of one such convert, Mohamed Nidalha, regrets not instilling in his son Reda moderate Islamic teachings as he was growing up in the Netharlands. The 20-year-old, who once liked girls and discos, suddenly changed after contact with extremist recruiters in neighbouring belgium. Recruiting new converts is key to the strategy of Islamic State militant group leader Abu Bakr Al-Baghdadi.