China, under pressure from Washington over North Korea's missile tests, said its chief negotiator would visit Pyongyang next week.
Pyongyang's statement came as the United States and Japan united against a UN Security Council split over whether to impose sanctions on North Korea for the missiles it fired on Wednesday.
North Korea's official KCNA news agency quoted a foreign ministry spokesman as saying: "The KPA will go on with missile launch exercises as part of its efforts to bolster deterrent for self-defence in the future.
"The DPRK will have no option but to take stronger physical actions of other forms, should any other country dare take issue with the exercises and put pressure upon it."
DPRK stands for the Democratic People's Republic of Korea.
Officials say North Korea launched at least six missiles from its east coast early on Wednesday and a seventh about 12 hours later.
The missiles included a long-range Taepodong-2, which some analysts believe could reach Alaska.
US officials said it flew for less than a minute and splashed into the sea west of Japan.
South Korea's defence minister told a parliamentary committee that an analysis of equipment and personnel being moved in and out of a missile-launch site in North Korea suggested the possibility of further launches.
A Japanese newspaper reported on Friday that North Korea targeted waters near the US state of Hawaii in the Pacific Ocean when it fired the long-range missile.
Japan's Sankei newspaper said that Japanese and US defence officials had concluded that the Taepodong-2 had been aimed at Hawaii, after analysing data collected by intelligence equipment.
The newspaper quoted unidentified Japanese and US government officials who decided that the missile was pointed at Hawaii from the angle of its nose cone immediately after its launch and the altitude it reached, the newspaper said.
The South Korean daily, Chosun Ilbo, cited a government official as saying the North might be looking to launch three or four more intermediate-range missiles.
NBC News, citing unnamed US officials, said preparations seemed to be under way for a second Taepodong test, but the weapon was not yet at the launch pad.
"We need China to be very, very firm with their neighbours"
Christopher Hill, US negotiator
Analysts say it could take weeks to prepare a Taepodong-2 for firing. Tokyo said it did not expect an imminent launch.
Junichiro Koizumi, the Japanese prime minister, and the US president, George Bush, agreed to work together for a UN resolution demanding that nations halt funds and technology that could be used for Pyongyang's missile programme.
"I think we've got to plan for the worst and hope for the best," Bush said. "And planning for the worst means to make sure that we continue to work with friends and allies, as well as those who've agreed to be a part of the six-party talks, to continue to send a unified message."
This US-Japan agreement came after Russia and China objected to imposing sanctions on North Korea.
Alexander Losyukov, the Russian ambassador to Japan, told reporters in Tokyo that sanctions could prevent a revival of six-country talks on ending Pyongyang's nuclear arms programme, which have been stalled since last November.
Christopher Hill, the US negotiator, said the launches had united opinion against Pyongyang, but he implied that Washington was seeking a tougher line from China.
"We need China to be very, very firm with their neighbours and frankly with their long-term allies, the North Koreans, on what is acceptable behaviour and what is not acceptable behaviour," Hill said.
Hill met Wu Dawei, the Chinese vice-foreign minister just hours after their presidents spoke by phone in an attempt to secure a co-ordinated response to the tests.
Bush also spoke with John Howard, the Australian prime minister, by phone. Australia has responded to the launch by deciding to reduce its diplomatic ties with North Korea, according to local media.
Australia is one of a handful of countries that maintains limited diplomatic relations with Pyongyang.
The North Korean spokesman said Pyongyang did not feel bound by a ban on missile testing and had the right to conduct such tests in the interests of self-defence.
North-South talks off
South Korea has rejected an offer of military talks with the North following the missile launch.
"Our side judged that it is not an appropriate time," the South Korean defence ministry said. "We notified the North that we would propose a date at an appropriate time later."
The working-level meeting would have been aimed at setting up talks between generals of the two militaries.
The two sides held the last high-level military talks in May, but failed to produce any agreement because of a dispute over sea borders.