DUBLIN (AP) — Diplomatic efforts to end Syria's civil war moved forward Thursday with U.S. Secretary of State Hillary Rodham Clinton joining Russia's foreign minister and the U.N. peace envoy to the Arab country for extraordinary three-way talks that suggested Washington and Moscow might finally unite behind a strategy as the Assad regime weakens.

In Washington, Defense Secretary Leon Panetta said intelligence reports raise fears that an increasingly desperate Syrian President Bashar Assad is considering using his chemical weapons arsenal — which the U.S. and Russia agree is unacceptable. It was unclear whether he might target rebels within Syria or bordering countries, but growing concern over such a scenario was clearly adding urgency to discussions an ocean away in Ireland's capital.

On the sidelines of a human rights conference, Clinton gathered with Russian Foreign Minister Sergey Lavrov and mediator Lakhdar Brahimi for about 40 minutes to look for a strategy the international community could rally around to end Syria's 21-month civil war.