The CIA, Department of Defense and Air Force declined to comment.
More than a dozen people were killed and more than 100 people injured in a large-scale overnight Russian missile and drone strike on Ukraine, officials said.
At least four people were killed and 91 people injured across Ukraine after Russia launched a major missile and drone strike on the country, Ukrainian officials said.
Russian President Vladimir Putin had been calling for the short pause in attacks to take place over his country's "Victory Day" holiday on May 9.
Russia continued to strike Ukrainian positions with drones after a Kremlin-declared Easter ceasefire took effect on Saturday, a Ukrainian military officer said.
Robert Mueller, the FBI director and special counsel who investigated ties between Russia and Donald Trump's presidential campaign, has died.