Secretary of the State Hillary Rodham Clinton said that Russia is putting its "vital interests" and relationships in the Middle East at risk if it does not act constructively on Syria, which, she said, is "spiraling towards civil war."
Clinton's warning came a day after she accused Russia of providing a shipment of attack helicopters to Syria—a claim that Russian foreign minister Sergey Lavrov denied. Lavrov, in turn, accused Washington of giving arms to rebels.
"The United States has provided no military support to the Syrian opposition," Clinton said Wednesday. "None."
The United States and United Nations are attempting to put pressure on Russia to help end the 15-month conflict that has left more than 13,000 Syrians dead.
On Tuesday, Clinton said that the conflict there could escalate without a regime change.
"We are concerned about the latest information we have that there are attack helicopters on the way from Russia to Syria," Clinton said Tuesday, echoing remarks she made last week calling for Syrian President Bashar Assad to be removed from power.
"We are watching this very carefully," Clinton said.
[Slideshow: Crisis in Syria]
During a meeting with envoys from 16 European, Turkish and Arab countries in Istabul last week, Clinton accused Assad of doubling down on "simply unconscionable" violence after reports that at least 78 people—including women and children—had been killed by pro-government forces near Hama the day before.
"We're disgusted by what we see happening," Clinton said. "The regime-sponsored violence that we witnessed again in Hama yesterday is simply unconscionable. Assad has doubled down on his brutality and duplicity, and Syria will not, cannot be peaceful, stable or certainly democratic until Assad goes."