beirut u.s. missile attack syrian airbase friday elevate political tensions expect lead military escalation say senior official military alliance support president bashar al-assad doubt leave great tension political level expect military escalation currently believe go towards big war region official tell reuters official non-syrian speak condition anonymity say personal assessment say spokesman alliance assad back six-year-old war russia iran shi ite militias countries include iraq lebanon afghanistan doubt russians escalate towards military friction americans official say u.s. attack lead military escalation say pro-damascus official