Besieged Ukrainians held out hope Monday that renewed diplomatic talks with Russia might open the way for more civilians to evacuate, a day after Moscow escalated its offensive by shelling areas perilously close to the Polish border. Ukraine’s leader warned that the attacks could expand to neighbouring countries.

Russian missiles pounded a military base in western Ukraine on Sunday, killing 35 people in an attack on a facility that served as a crucial hub for cooperation between Ukraine and the NATO countries supporting its defence. It raised the possibility that the alliance could be drawn into the fight. The attack was also heavy with symbolism in a conflict that has revived old Cold War rivalries and threatened to rewrite the current global security order.

Ukrainian President Volodymyr Zelenskyy called it a “black day,” and again urged NATO leaders to establish a no-fly zone over the country, a plea that the West has said could escalate the war to a nuclear confrontation.