Israel was drawn into the Syrian civil war for the first time on Sunday, firing warning shots into the neighboring country after a stray mortar shell from across the border hit an Israeli military post. The Israeli military said the mortar fire caused no injuries or damage at the post in the Golan Heights, which Israel captured from Syria in the 1967 Mideast war and then annexed. But in recent weeks, incidents of errant fire from Syria to the north have multiplied, leading Israel to warn that it holds Syria responsible for fire on Israeli-held territory.