Fighting around the capital city has intensified over the past week, and Western officials have begun speaking about faster change on the ground in a 20-month-old conflict that has killed 40,000 people.

But Russia and the United States, the superpowers that have backed the opposing sides in the conflict, both played down the chance of a diplomatic breakthrough after talks aimed at resolving their differences.

"I don't think anyone believes that there was some great breakthrough," U.S. Secretary of State Hillary Clinton said of a meeting with Russia's Foreign Minister Sergei Lavrov and international mediator Lakhdar Brahimi.