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.
July 4 fireworks
North Korea, whose government pays close attention to symbolic gestures, chose July 4, the day the United States marks Independence Day, for the launch. It came just hours after the US space shuttle Discovery blasted off from Florida.
"It got everybody's attention on the Fourth of July. (North Korean leader) Kim Jong-Il can set off fireworks, too," said John Pike, director of the security website GlobalSecurity.org.
Japan said it would consider immediate economic sanctions against North Korea. NHK television reported that the government had banned visits by North Korean ferries for six months.
The Japanese yen and the South Korean won both slipped against the dollar on the launch news, with Tokyo and Seoul stock markets also lower. In Seoul, the government said South Korean authorities would take action if necessary.
Tokyo also called on Pyongyang to return to six-country talks on ending its nuclear weapons programme, which have been stalled since November.
"It is regrettable and we protest strongly against North Korea for going ahead with a launch despite warnings from relevant countries, including Japan," Japanese Chief Cabinet Secretary Shinzo Abe said in Tokyo.
"It is a serious problem from the standpoint of our national security, peace and stability of the international community and proliferation of weapons of mass destruction."
In a separate incident, but underlining the tensions in the region, Japan summoned South Korea's ambassador to demand Seoul halt a survey of disputed waters that began earlier in the day.
South Korea and Japan came close to a high-seas showdown in April when Tokyo said it planned a survey in waters near a desolate outcrop of islands called Tokto in Korean and Takeshima in Japanese, but tensions eased after talks.
North Korean media made no mention of the multiple launches, Japanese reporters in Pyongyang said. Television channels had no programming on Wednesday morning, they said, and state radio led its bulletins on Kim Jong Il's visit to a tyre factory.
Experts say the Taepodong-2 has a possible range of 3,500-4,300 km.
A US State Department official said the long-range missile had failed 40 seconds after it was launched. A senior South Korean security official said the Taepodong-2 had splashed down in the Sea of Japan, off the peninsula's east coast.
Such a flop, said Daniel Pinkston, director of the East Asia non-proliferation programme for the California-based Centre for Non- proliferation Studies, would be a blow to Pyongyang.
"If there was failure that early on in the flight, there is no way they could make any claims of test-launching a satellite as they did in 1998. They will not be able to exploit the propaganda value of that after that type of failure," he said.
Experts say that Pyongyang is developing long-range missiles to have the capability one day to deliver a nuclear bomb, but that it is years away from acquiring such a weapons system.