WASHINGTON - The United States expelled Syria's top diplomat in Washington on Tuesday following what it described as the "despicable" massacre of more than 100 civilians in a Syrian town. The US continued to rule out military intervention, while France said military action was a possibility, but only if backed by the United Nations.State Department spokeswoman Victoria Nuland said Syrian Charge d'Affaires Zuheir Jabbour had been given 72 hours to leave the country, part of a wave of expulsions of Syrian diplomats from Western capitals."We hold the Syrian government responsible for this slaughter of innocent lives," Nuland said, calling the Houla attack "the most unambiguous indictment to date" of Damascus' refusal to implement UN resolutions calling for a peaceful resolution to the conflict.Syrian officials have denied any army role in the massacre, one of the worst single incidents in the conflict.The White House on Tuesday said again that it did not believe the time was right for military intervention in Syria, and rejected calls by Republican presidential candidate Mitt Romney for more direct steps to end Assad's rule."We do not believe that militarization, further militarization of the situation in Syria at this point is the right course of action. We believe that it would lead to greater chaos, greater carnage," White House spokesman Jay Carney said.French President Francois Hollande said on Tuesday that military action could be possible but only if it was backed by a UN resolution.The crisis in Syria is one of the first diplomatic tests for Hollande after predecessor Nicolas Sarkozy's high-profile role in last year's crises in Libya and Ivory Coast. Hollande will meet Putin in Paris on Friday."It is not possible to allow Bashar Assad's regime to massacre its own people," Hollande told France 2 television, referring to Syria's president."Military intervention is not excluded provided it is carried out under the auspices of international law, namely via a Security Council resolution."While the moves were symbolically important and aimed at increasing Syrian President Bashar Assad's isolation, the Obama administration continued to resist any US military intervention in Syria.The killings in the village of Houla, some of which the UN peacekeeping chief on Tuesday said bore the hallmarks of pro-Assad militias, have increased pressure on Western government to halt more than a year of bloodshed in Syria.On the diplomatic front, Australia, Canada, France, Germany, Italy, Spain and the United Kingdom took similar steps against Syrian diplomats in those countries in a coordinated move."We took this action in response to the massacre in the village of Houla - (the) absolutely indefensible, vile, despicable - massacre against innocent children, women, shot at point-blank range by regime thugs, the Shabiha," Nuland told reporters, referring to pro-government militia.In a separate statement, Nuland described Friday's attack on the town of Houla as a "vicious assault involving tanks and artillery - weapons that only the regime possesses.""There are also reports that many families were summarily executed in their homes by regime forces," Nuland said.