Russia denied Wednesday it was behind hoax bomb threats during voting in the U.S. presidential election and rejected reports of an alleged Russian plot to place incendiary devices on planes to the United States.

Hoax bomb threats, many of which appeared to originate from Russian email domains, were directed Tuesday at polling locations in five battleground states – Georgia, Michigan, Arizona, Wisconsin and Pennsylvania – as Election Day voting was under way, the FBI said.

Security officials said separately that parcels that exploded at logistics depots in Europe were part of a test run for a Russian plot to trigger explosions on cargo flights to the United States.