UNITED NATIONS — Secretary-General Ban Ki-moon demanded international action to stop the war in Syria, telling a somber gathering of world leaders Tuesday that the 18-month conflict had become “a regional calamity with global ramifications.”

In his state of the world speech at the opening of the U.N. General Assembly’s annual ministerial meeting, Ban said he was sounding the alarm about widespread insecurity and injustice, inequality and intolerance in many countries.