The transfer of more than a million barrels of oil from an aging tanker moored off the coast of war-torn Yemen has been completed, avoiding an environmental disaster, the United Nations said Friday. In a statement, Farhan Haq, the deputy spokesman for U.N. Secretary-General Antonio Guterres, said the operation had prevented a “monumental environmental and humanitarian catastrophe.” An international team began siphoning the oil from the dilapidated vessel known as FSO Safer on July 25.