The collapse follows nationwide blackouts last year that plunged Cuba's frail power-generating system into disarray.

The call, scheduled for Tuesday, will be the first known conversation between the two leaders since Mr. Putin laid out numerous conditions for a cease-fire with Ukraine.

But by early Saturday night, neither of Cuba's two largest power plants - Felton, in Holguin province, and Antonio Guiteras, in Matanzas - was generating electricity, leaving the majority of the ...