North Korea test-fired seven missiles on Wednesday, including a long-range weapon said to be capable of reaching Alaska, ratcheting up tensions in north Asia and drawing international condemnation.
The last launch, at 5:22 pm (1352 IST), took place much after the launch of the other six missiles.
North Korea had test-fired six missiles earlier, including one capable of reaching US soil, though all splashed down in the Sea of Japan (East Sea), according to US and Japanese officials.
The long-range Taepodong-2 multi-stage missile apparently failed 40 seconds into its flight, US officials said.
The UN Security Council was to meet later in the day, at Japan's request, to discuss the latest move by the reclusive Stalinist state, a French spokesman at the United Nations said.
South Korea's military stepped up its alert level after the launch, a news agency cited a military source as saying.
The two Koreas are technically still at war more than half a century after the inconclusive truce, which halted the 1950-1953 Korean conflict. Some 30,000 US troops remain in South Korea under a mutual defence treaty.
The United States warned North Korea against any more provocative acts, and said Washington would take necessary measures to protect itself and its allies.
"The United States strongly condemns these missile launches and North Korea's unwillingness to heed calls for restraint from the international community," White House spokesman Tony Snow said in a statement.
The missile launches "demonstrate North Korea's intent to intimidate other states by developing missiles of increasingly longer ranges", he said.
"We are consulting with international partners on next steps."
US National Security Adviser Stephen Hadley said the multiple firings posed no threat to US territory.
He said the launches might have been a Pyongyang attempt to steal the spotlight away from Iran, which has been the main focus of US nuclear diplomacy in recent months.
"Obviously, it is a bit of an effort to get attention, perhaps because so much attention has been focused on the Iranians," Hadley said.
But like many US officials, he said it was impossible to be sure about Pyongyang's motives.