Ukraine called on Friday for full membership in NATO, its strongest plea yet for Western military help, after accusing Russia of sending in armored columns that have driven back its forces on behalf of pro-Moscow rebels.

Russian President Vladimir Putin, defiant as ever, compared Kiev's drive to regain control of its rebellious eastern cities to the Nazi invasion of the Soviet Union in World War II. He announced that rebels had succeeded in halting it, and proposed that they permit surrounded Ukrainian troops to retreat.

Speaking to young people at a summer camp, Putin told his countrymen they must be "ready to repel any aggression toward Russia." He described Ukrainians and Russians as "practically one people" — language that Ukrainians say dismisses the very existence of their thousand-year-old nation.