(Reuters) – Islamic State militants have executed Syrian army soldiers and are holding a group hostage after capturing an air base in northeast Syria at the weekend, pictures posted on social media by supporters showed on Wednesday. Islamic State, an offshoot of al Qaeda, stormed Tabqa air base near Raqqa city on Sunday after days of fighting with the army that cost more than 500 lives, according to monitoring group the Syrian Observatory for Human Rights. Tabqa […]