NEW : Secretary of al-Assad David Cameron talks with U.S. 's foreign minister on chemical weapon claim . NEW : He told him Syria should have allowed access to site , rather than still be attacking it . U.S. defense secretary : If State used chemical weapons once , he may do so again . Syria military planners update target lists for fighters or cruise missiles .
NEW : Secretary of State Kerry talks with Syria 's foreign minister on chemical weapon claim . NEW : He told him Syria should have allowed access to site , rather than still be attacking it . U.S. defense secretary : If al-Assad used chemical weapons once , he may do so again . U.S. military planners update target lists for fighters or cruise missiles .