By Matt Spetalnick and Jeff Mason WASHINGTON (Reuters) - President Barack Obama warned Syria on Friday that its use of chemical weapons would be a "game changer" for the United States but made clear he was in no rush to intervene in the Syrian civil war on the basis of evidence he said was still preliminary.

By David Brunnstrom BRUSSELS (Reuters) - U.S. Secretary of State John Kerry said on Tuesday he and Russian Foreign Minister Sergei Lavrov had agreed to look for ways to revive a Syrian peace plan, but admitted that doing so would be extremely difficult. Kerry, speaking after talks with Lavrov and NATO colleagues in Brussels, also backed away from earlier comments suggesting he was calling for increased NATO contingency planning on Syria.

BRUSSELS (Reuters) - U.S. Secretary of State John Kerry said on Tuesday that NATO needed to consider its role in the Syrian crisis, including how it would respond to a potential chemical weapons threat. "We need to continue to consider NATO's role as it relates to the Syrian crisis," Kerry said in a statement prepared for a meeting of NATO foreign ministers in Brussels, adding that the planning that the alliance had already done was appropriate.

Pope Francis is praying for the liberation of two Orthodox bishops kidnapped by rebels in northern Syria, the Vatican said on Tuesday, a day after Syrian state media reported the abduction. Francis "is following developments with deep participation and intense prayer for their well-being and liberation," the Vatican's spokesman, Federico Lombardi, told reporters. The incident is "a dramatic confirmation of the tragic situation of the population of Syria and its Christian communities," Lombardi said.