The European Union's anti-terror chief says that hundreds of Europeans are now fighting with rebel forces in Syria.
There's concern among EU intelligence agencies that some the fighters could join jihadi groups linked to al-Qaida and later return to Europe to launch terrorist attacks.
The BBC's Duncan Crawford met with one Belgian family that says their son has traveled to Syria to join rebels fighting against Bashar al-Assad's regime.
Meantime, Syrian state media and anti-government activists say the minaret of the famed Umayyad Mosque in Aleppo (also called the Great Mosque) has been destroyed.
Syria says rebels from the al-Qaida-linked group Jabhat al-Nusra blew it up. Rebels say a Syrian tank fired a shell that "totally destroyed" the minaret.
The 12th century mosque and nearby medieval market are centerpieces of Aleppo's walled Old City - listed as a UNESCO World Heritage Site - but heavily damage during the fighting.
This segment aired on April 24, 2013.