Receive Breaking News updates as they occur
By Pavel Polityuk and Alastair Macdonald KIEV (Reuters) - Ukraine's government said on Wednesday the United States had promised to stand by it in the face of aggression, and announced that it would press ahead with a security operation to crack down on pro-Russian armed groups. After a lull for the Easter religious holiday, officials in Kiev decided to renew what they call an "anti-terrorist operation" against separatist militias who have seized control of about a dozen public buildings in eastern Ukraine. But it was unclear what steps, in reality, Kiev could take to restore its authority in the mainly Russian-speaking east, without wrecking an international deal, signed last week in Geneva, designed to defuse the stand-off. The crisis over Ukraine, now in its fourth month, has dragged Russia's relations with the West to their lowest level since the Cold War.