Watch the moment North Korea announced its first hydrogen bomb test.

American officials still “cannot confirm these claims at this time,” according to a White House spokesman, though if true they would represent a significant advance in North Korea’s nuclear capabilities and a new diplomatic challenge for both the U.S. and North Korea’s neighbors. The announcement was delivered on North Korean state television with typical fanfare and belligerence: “We will not give up a nuclear program as long as the United States maintains its stance of aggression,” the anchor says.