UNITED NATIONS (AP) — 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 sharp contrast to the U.N. chief, President Barack Obama pledged U.S. support for Syrians trying to oust President Bashar Assad — "a dictator who massacres his own people."

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