A top U.S. envoy arrived in Tokyo on Sunday to rally a united international front against North Korea's recent missile tests, but cracks were already appearing over a Japanese proposal to slap sanctions against the communist state.

The visit comes ahead of a pivotal U.N. Security Council showdown over a Japanese-backed resolution that would open the door for punitive sanctions.

Japan vowed Sunday not to compromise over the stern wording in its resolution, despite resistance from China, and South Korea's apparent wavering over sanctions.

North Korea also issued fresh threats that attempts to rein in its military exercises could spark a war.

China and Russia, two of North Korea's traditional allies, remain two veto-wielding permanent members of the Security Council who have voiced opposition to the resolution, which Japan hopes to put to a vote on Monday.

But U.S. Assistant Secretary of State Christopher Hill, who arrived in Japan after stops in Beijing and Seoul, said the major players are presenting a unified message to North Korea, which rattled Northeast Asia and beyond by test-firing a volley of seven missiles into the Sea of Japan on Wednesday. Among the missiles was at least one believed to be capable of striking U.S. shores.

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"I don't see any splintering. On the contrary, I see a very clear message," Hill said after arriving in Tokyo, where he was expected to hold talks with Foreign Minister Taro Aso on Monday. "All countries are showing resolve in the ways that they can."

Song Min-soon, South Korea's presidential security adviser, however, told The Associated Press that Seoul was not convinced sanctions would stop North Korea's missile efforts, adding more work was needed to see whether that was the best step to take.

"We first need to determine if such measures will be effective in preventing the North's missile proliferation," Song said, refusing to say clearly whether Seoul supported or opposed the idea. Seoul has already suspended food and fertilizer aid to the North after the missile tests.

Japan, which sits within easy range of North Korean missiles, said Sunday it won't compromise on the U.N. resolution, which was submitted Friday to the Security Council and prohibits nations from procuring missiles or missile-related "items, materials goods and technology" from North Korea, or from transferring financial resources connected to the North's program.

"To compromise because of one country which has veto power, even though most other countries support us, sends the wrong message," Aso told national broadcaster NHK. "We can't alter our stance."

Aso said there is a possibility that Russia will abstain from voting on the resolution, leaving China in a pinch as to whether to be the sole country voicing opposition. Nine of 15 votes on the Security Council are needed to pass the resolution and Aso called a 14 to 1 vote the worst outcome for China. The United States, Britain and France have expressed support for the resolution.

"China will be backed into a corner," Aso said later on a TV Asahi talk show. "It's only common sense not to do that."

As behind-the-scenes negotiations gathered pace, North Korea's ambassador to Australia meanwhile warned that international attempts to halt his nation's missile tests could trigger war.

In an article written by Ambassador Chon Jae Hong that appeared in The Sunday Herald Sun newspaper in the southern city of Melbourne, he defended Pyongyang's missile launches as routine military drills.

"It is a lesson taught by history and a stark reality of international relations, proven by the Iraqi crisis, that the upsetting of the balance of force is bound to create instability and spark even a war," Chon said.

North Korea "will have no option but to take stronger physical actions of other forms, should any country dare take issue with the exercises and put pressure upon it," he added.

Supporters of the Japan-backed U.N. resolution decided at a meeting Friday afternoon not to call for a vote over the weekend after some council members asked for more time to weigh up the options.

The draft is tougher than previous versions, and Aso said it was crucial to get a binding resolution passed this time.

A previous missile test by North Korea in 1998 was only followed by a nonbinding U.N. censure, and the isolated communist country has only used the intervening years to improve its missile technology, Aso said.

"We have to learn from the past," Aso said.

Later in the day, Aso and Chinese Foreign Minister Li Zhaoxing held a 35-minute telephone call to discuss the U.N. Security Council response, Kyodo News agency said. Details of the talks were immediately known, but Aso is believed to have asked China not to use its veto power to shoot down the North Korea resolution, the report said.

South Korea has taken a mixed approach toward the North. It condemned the tests and cut off some aid, but has also called for "patient dialogue" and plans to go ahead with bilateral talks with Pyongyang later this week.

A South Korean delegation still plans to host meetings from Tuesday to Friday in the southern port city of Busan. The Cabinet-level talks are the highest-level regular contacts between the two Koreas, and were begun after a North-South summit in 2000.