The White House today said it took a new warning from North Korea that it was in a state of war with South Korea seriously, but said Pyongyang's threats were following a familiar pattern.
"We've seen reports of a new and unconstructive statement from North Korea," said Caitlin Hayden, spokeswoman for the National Security Council.
"We take these threats seriously and remain in close contact with our South Korean allies."
North Korea earlier delivered the latest in a string of dire threats that have drawn a tough response from Seoul and Washington, and sparked international concern that tensions on the peninsula could get out of control.
Pyongyang said it had formally entered a "state of war" with South Korea and warned that any provocation would swiftly escalate into a nuclear conflict.