KIEV, Ukraine — Separatist rebels retreated Monday from positions throughout eastern Ukraine, apparently blowing up bridges as they went, and began building barricades in the two largest cities, Donetsk and Luhansk, in anticipation of a final stand against advancing government troops.
Ukrainian officials said they had succeeded in sealing the previously porous border with Russia, stopping the influx of new weapons and fighters and prompting bitter complaints from separatist leaders about being sold out by their patrons in Moscow.
The action 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 prompting a reaction from Moscow.
Ukrainian President Petro Poroshenko called off a cease-fire last week and vowed to defeat the rebels on the battlefield. But that has raised the prospect of protracted and bloody urban warfare with significant civilian casualties.
Russian President Vladimir Putin, who warned last week he would not stand by while the safety of Russians was endangered, did not comment on the deteriorating situation. That was left to Foreign Minister Sergey Lavrov, who complained about damage to civilian areas but mentioned nothing about possible military action. The Kremlin appears to have taken that option off the table, in favor of a negotiated settlement that might install close allies of Russia as the governors of Donetsk and Luhansk.
"It is in our common interest to stop the bloodshed as soon as possible," Lavrov said at a news conference in Sofia, Bulgaria. "Our position is that there can be no reason whatsoever to postpone the cease-fire. The fighting is inflicting great suffering on the civilian population, as a result of which the outflow of refugees is increasing and civilian infrastructure is being destroyed."
In an apparent bid to slow the oncoming troops, the pro-Russian insurgents blew up two bridges on the road to Donetsk from Slovyansk and Kramatorsk, two long-occupied provincial cities where rebels were ousted over the weekend after a fierce bombardment.