The United States President Barack Obama threatened fresh sanctions against Moscow if it escalates the crisis over Ukraine, as pro-Russia separatists faced today's deadline from Kiev to lay down their arms.The White House said in a statement that the president stressed that the United States, the European Union and other global partners must be prepared to meet further Russian escalation with additional sanctions,The statement came after Obama and German Chancellor Angela Merkel spoke by phone yesterday.The United States also delivered the warning to Russia at World Bank, IMF meetings in Washington, amid worries that a spiralling Ukraine crisis could hurt the world economy.Ukraine's embattled leaders, scrambling to hold their splintered country together after the annexation of Crimea, on Thursday offered amnesty to pro-Russian separatists occupying eastern state buildings if they lay down their arms and halt afour-day siege.Acting President Oleksandr Turchynov, in power since pro-Russian leader Viktor Yanukovych was ousted in February, told lawmakers that Ukraine's latest secessionist crisis could be resolved peacefully.