"We don't really have anything more to add to the reports about the explosion on the bridge," White House national security spokesman John Kirby told ABC's "This Week" program."By calling up hundreds of thousands of reservists, by politically annexing, or at least trying to annex four areas of Ukraine, he has shown every indication that he is doubling down," Kirby added.This, said Kirby, "is why, quite frankly, we are in touch almost daily with the Ukrainians and we’re going to continue to provide them security assistance."Largely echoing the White House's comments last week after U.S. President Joe Biden referenced the possibility of nuclear "Armageddon," Kirby said the United States had no indication that Putin had made a decision to use nuclear weapons and that there was no reason to change the U.S. strategic posture."The president was reflecting the very high stakes that are in play right now ... when you have a modern nuclear power, and the leader of that modern nuclear power, willing to use irresponsible rhetoric the way Mr. Putin has," Kirby said."