Inspectors found "clear and convincing evidence" that the nerve agent sarin was delivered by surface-to-surface rockets "on a relatively large scale" in the August 21 attack on a Damascus suburb, Ban said Monday.
"It is the most significant confirmed use of chemical weapons against civilians since Saddam Hussein used them in Halabja in 1988," Ban said, referring to the chemical attack against Kurds in northern Iraq that killed thousands, mostly civilians, "and the worst use of weapons of mass destruction in the 21st century," Ban said. "The international community has a responsibility to ensure that chemical weapons never re-emerge as an instrument of warfare."
But on Tuesday, Ban said it was "for others to decide whether to pursue this matter further to determine responsibility and accountability."
The diplomatic quarrel over just who may have been responsible for the chemical weapons attack came as the toll from conventional weapons continued to mount. The opposition Local Coordination Committees of Syria reported that 70 people -- including four children and seven women -- were killed Tuesday nationwide.
Syrian-Turkish border tension
A blast rocked the Syrian side of the Turkish-Syrian border Tuesday, Turkey's semiofficial Anatolian news agency reported.
Video shot by activists showed torrents of black smoke emerging from blazing vehicles at the crossing as survivors tried to help victims.
The LCC said the attack wounded many people.
The explosion, which happened near a border gate, comes a day after Turkish planes shot down a Syrian helicopter crossing into Turkey. It came down on Syrian territory, Turkish Deputy Prime Minister Bulent Arinc said.
Syria's state news agency SANA said the helicopter was watching for "terrorists" crossing the border and erroneously strayed into Turkish airspace, but was on its way back across the border when shot down.