By Louis Charbonneau
UNITED NATIONS, Aug 27 (Reuters) - A joint mission of the United Nations and the global anti-chemical arms watchdog that has overseen the destruction of Syria's toxic gas stocks will shut down on Sept. 30 though a successor unit will continue investigating, the U.N. chief said.
Last week the Pentagon said a specially equipped U.S. ship had finished neutralizing all 600 metric tons of the most dangerous of Syria's chemical weapons components surrendered to the international community this year to avert threatened air strikes.
With the bulk of the elimination work completed, U.N. Secretary-General Ban Ki-moon wrote to the president of the Security Council, British Ambassador Mark Lyall Grant, that a joint mission of the U.N. and Organization for the Prohibition of Chemical Weapons (OPCW) would shut down next month.
"With the completion of the destruction of all declared priority chemical weapons materials, and following consultations with the Director-General of the OPCW, we will bring the Joint Mission to a close on 30 September 2014," Ban wrote in the letter, obtained by Reuters on Wednesday.
"Successor arrangements will be in place at that time to ensure a seamless transition," Ban added. He did not elaborate as details of the arrangements were still being worked out.
In a monthly report on Syria attached to Ban's letter, the OPCW said that its own fact-finding team was "continuing its work to establish the facts surrounding the allegations of the use of toxic chemicals, reportedly chlorine, for hostile purposes in the Syrian Arab Republic."
A U.N. commission of inquiry on Wednesday accused the Syrian government of dropping barrel bombs on civilian areas, a war crime under international law. The bombs included some believed to contain the poison gas chlorine in eight incidents in April, the investigators said in their latest report.
Ban said that until Syria's entire chemical weapons program has been eliminated he would continue to use his authority to monitor compliance with a Security Council resolution from last year that demanded the elimination of all Syrian poison gas stocks and production facilities.
Syria agreed last September to a Russian proposal to give up its chemical weapons to avert threatened military strikes by the United States and France, which accused the Syrian leadership of using the arms against opponents of President Bashar al-Assad.
An August 2013 sarin gas attack in a Damascus suburb killed well over 1,000 people, including many women and children, the worst chemical weapon attack in a quarter century. The government and rebels blamed each other for the incident. Western powers blame Assad for the attack while Russia says rebels were likely responsible.
Ban said negotiations with the OPCW and Syria on arrangements for the destruction of 12 remaining chemical weapons production facilities were still underway.
Western members of the Security Council have long voiced concerns about ambiguities and discrepancies in Syria's original declaration of its poison gas arsenal, which Damascus submitted last year to the OPCW.
Syria's civil war is now in its fourth year. (Reporting by Louis Charbonneau; Editing by Tom Brown)