DUBLIN – 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.

“I think there is no question that we remain very concerned, very concerned,” Panetta said, “that, as the opposition advances, in particular in Damascus, that regime might very well consider the use of chemical weapons.”

It was unclear whether Assad might target rebels within Syria or bordering countries, but growing concern over such a scenario was clearly adding urgency to discussions 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.

“We have talked a little bit about how we can work out hopefully a process that will get Syria back from the brink,” Brahimi said after the meeting ended.

The experienced Algerian diplomat, representing the global body and the Arab League, said he would put together a peace process based on a political transition strategy the U.S. and Russia agreed on in Geneva in June. Then, the process quickly became bogged down over how the international community might enforce its conditions.

“We haven’t taken any sensational decisions,” Brahimi said. “But I think we have agreed that the situation is bad and we have agreed that we must continue to work together to see how we can find creative ways of bringing this problem under control and hopefully starting to solve it.”

The former Cold War foes have fought bitterly over how to address the conflict, but Clinton stressed before the meeting that they shared a common goal.

“We have been trying hard to work with Russia to try to stop the bloodshed in Syria and start a political transition for a post-Assad Syrian future,” Clinton told reporters in Dublin.