By Steve Holland
WASHINGTON (Reuters) - President Barack Obama took U.S. concerns about Syrian chemical weapons to Russian President Vladimir Putin on Monday, reaching out to one of the Syrian government's staunchest allies.
The United States is trying to determine the facts around alleged Syrian use of chemical weapons. Last week U.S. officials said they had "varying degrees of confidence" that Syria had likely used the nerve agent sarin on a small scale against rebel fighters.
If proved with certainty, the chemical weapons' usage could triggered unspecified U.S. actions against the Syrian government. Russia has been one of the Syrian government's staunchest allies.
"President Obama and President Putin reviewed the situation in Syria, with President Obama underscoring concern over Syrian chemical weapons," a White House statement said.
The two leaders agreed to stay in touch on the issue and that Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov would continue discussions on Syria.
White House spokesman Jay Carney said the United States would proceed in a deliberate fashion in determining whether forces loyal to Syrian President Bashar al-Assad used chemical weapons to attack his own people.
Obama has vowed that all options will be considered if Syria is shown to have used chemical weapons but the White House is worried about the prospect of acting without definitive proof and aides say formulating a U.S. response will take time.
"It's very important that we take the information that's been gathered thus far and build upon it, because an assessment of varying degrees of confidence is not sufficient upon which to base a policy reaction," Carney said.
He said a U.N. team was ready to deploy to Syria in 24-48 hours to investigate chemical weapons allegations, if the Assad government let it in.
(Reporting By Steve Holland and Roberta Rampton; Editing by David Brunnstrom)