As helicopter gunships opened fire on the northern city of Aleppo, the U.S.'s top defense official called for efforts to "bring the Assad regime down."<br/> <br />En route to Tunisia, U.S. Secretary of Defense Leon Panetta.<br/> <br />SOUNDBITE: U.S. Secretary of Defense Leon Panetta saying:<br/> <br />"If they continue this kind of tragic attack on their own people in Aleppo, I think it ultimately will be a nail in Assad's own coffin. What Assad has been doing to his own people and what he continues to do to his own people makes clear that his regime is coming to an end. It's lost all legitimacy."<br/> <br />Syria is expected be a major focus of his talks in Israel and Jordan, particularly with concerns about the security of the country's chemical and biological weapons sites and waves of Syrian refugees spilling into neighboring countries.<br/> <br />Deborah Gembara, Reuters
