As the Obama administration weighs worst-case scenarios for Syria, one stands out: a civil war that develops into a proxy battle between Arabs and the West on one side, and Russia and Iran on the other. US officials stress they do not want to play a military role in Syria, where President Bashar Al-Assad's crackdown on protests has killed more than 5,000 people and raised fears of a protracted power struggle in a country at the heart of the Arab world. But after US and Arab-led efforts to craft consensus in the UN Security Council on Syria's political transition were torpedoed by vetoes from Russia and China, some analysts say risks are growing that the international community will line up on opposite sides of a fratricidal war. The volatile ingredients are already in place. Resistance fighters known as the Free Syrian Army have pledged to liberate the country from Assad's rule. Activists call for armed support for rebels. And Syrian security forces are ratcheting up the violence, vowing to fulfill their president's threat to strike with an “iron fist” against the government's opponents. “”There is a risk of it could become a proxy conflict. It is already headed in that direction,” said Andrew Tabler, a Syria expert at the Washington Institute for Near East Policy. “I think you will see now different countries in the region betting on the Free Syrian Army. Already weapons have been coming in from Lebanon. You will now see more coming in from Jordan, from Turkey, from Iraq or from Russia. Everyone will start to operate in this environment.” US officials say their emphasis is on building support for Syria's beleaguered political opposition and possibly providing humanitarian relief for refugees as the fighting intensifies. For their part, Russia and Iran say they are urging Damascus to make reforms. But they reject what they describe as a Western-engineered attempt to overthrow the government of one of their closest allies. Some in Washington worry the situation may eventually edge toward a Cold War-style proxy conflict. “At the moment it is not something that is being discussed,” one U.S. official said on condition of anonymity. “That is not to say that at some point down the line it won't be.”