KIEV, Ukraine — A former Russian lawmaker who fled to Ukraine last year was gunned down on a sidewalk in Kiev on Thursday morning, the latest in a string of politically hued murders of critics of the Russian government abroad, going back more than a decade.

The killing coincided with a fire and explosion at a gigantic Ukrainian Army ammunition depot in the country’s east that the authorities blamed on Russia, suggesting an escalation of Russian special operations inside Ukraine.

Ukraine’s president, Petro O. Poroshenko, said it was “no accident” that the killing of the lawmaker, Denis N. Voronenkov, occurred at the same time as the ammunition depot explosion. Ukraine’s military said a drone may have touched off the blast, near the city of Kharkiv, sending tank shells firing in all directions and forcing the evacuation of 20,000 people.