KIEV/SLAVIANSK, Ukraine - An agreement reached last week to avert wider conflict in Ukraine was faltering as the new week began, with pro-Moscow separatist gunmen showing no sign of surrendering government buildings they have seized.

US and European officials say they will hold Moscow responsible and impose new economic sanctions if the separatists do not clear out of government buildings they have occupied across swathes of eastern Ukraine over the past two weeks.

US Vice President Joe Biden arrived in Kiev, where he is expected to announce a package of technical assistance. The visit is likely to be more important as a symbol of support than for any specific pledges Biden makes in public.

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