Ukrainian separatists blow up a bridge

KIEV, Ukraine — Separatist rebels retreated Monday from positions in eastern Ukraine, apparently blowing up bridges, and began building barricades in the two largest cities, Donetsk and Luhansk, in anticipation of a final stand against advancing government troops. While separatist leaders have complained bitterly about being sold out by their allies in Moscow, Ukrainian officials said Monday that they had succeeded in sealing the previously porous border with Russia, stopping the influx of new weapons and fighters. The action on Monday came after a series of surprising successes by Ukraine’s underequipped and underfunded military, which in recent days has driven the rebels from some strongholds that were seized early in the three-month rebellion. It has accomplished this without encountering strong resistance or a reaction from Moscow.