Flanked by almost 20 men with rifles, Omar Abu al-Chechen kneels on a carpet and delivers a rousing speech urging fellow Muslims to support the 'jihad' against Syrian President Bashar al-Assad. Dressed almost entirely in black, the militant from Russia's Chechnya region declares an Islamist state is within reach. Fellow fighters from the brigade of foreign militants he leads translate his Russian words into Arabic. "Jihad needs very many things. Firstly it needs money. Much is dependent on money today for jihad," said al-Chechen, his nomme de guerre, the leader of what rebels and websites call the Brigade of Migrants,...