The United States was seeking to take advantage of the Syrian situation to move forward a political transition in the Arab country, a State Department spokesman said Thursday.

Department spokesman Mark Toner made the remarks as the Syrian opposition forces are making steady gains in their 20-month conflict with the government led by President Bashar al-Assad.

"So as these events are accelerating on the ground and as pressure on the regime is increasing, you know, we're looking for opportunities to move to that political transition," Toner told reporters at a regular news briefing.

"But let's be very clear that, you know, we're not pushing the opposition to negotiate without clear guarantees," he added. "And first and foremost that means that for any transition, let's be very clear that Bashar al-Assad is not a part of that equation. He cannot remain in power."

U.S. Secretary of State Hillary Clinton met on Thursday with Russian Foreign Minister Sergei Lavrov and UN-Arab League joint envoy for Syria Lakhdar Brahimi in Dublin, Ireland, where the top American envoy said "Events on the ground are accelerating and we see that in many different ways."

Clinton and other high-ranking foreign diplomats will attend a meeting of the Friends of the Syrian People next week in Morocco on "how best to continue support for the Syrian opposition and on efforts to end the bloodshed," as the State Department put it.

NATO agreed on Tuesday to deploy Patriot missile batteries in Turkey to deter what it called possible Syrian missile attacks, a move that will bring American and European troops to the border area with Syria.