The United States says countries trading with North Korea were aiding its "dangerous nuclear intentions" as the United Nations Security Council mulled tough new sanctions and the isolated regime showed signs of planning more missile tests.
South Korea said it was talking to Washington about deploying aircraft carriers and strategic bombers to the Korean peninsula following the North's sixth and most powerful nuclear test on Sunday.
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At a Security Council meeting on Monday, US Ambassador Nikki Haley said North Korea's Kim Jong Un was "begging for war" and urged the 15-member group to adopt the strongest possible measures to deter him.
"War is never something the United States wants. We don't want it now. But our country's patience is not unlimited. We will defend our allies and our territory," Ms Haley said.
"The United States will look at every country that does business with North Korea as a country that is giving aid to their reckless and dangerous nuclear intentions."
Ms Haley said the United States will circulate a new Security Council resolution on North Korea this week and wants a vote on it next Monday.
China, a top trading partner with North Korea, and Russia called for a peaceful resolution to the crisis.
"China will never allow chaos and war on the (Korean) Peninsula," said Liu Jieyi, the Chinese ambassador to the United Nations.
Russia said peace in the region was in jeopardy.
"A comprehensive settlement to the nuclear and other issues plaguing the Korean peninsula can be arrived at solely through political diplomatic channels," Russia's UN Ambassador Vassily Nebenzia said.
North Korea has been under UN sanctions since 2006 over its ballistic missile and nuclear programs. Typically, China and Russia only view a test of a long- range missile or a nuclear weapon as a trigger for further possible sanctions.
US President Donald Trump had asked to be briefed on all available military options, according to his defence chief.
Officials said activity around missile launch sites suggested North Korea planned more missile tests.
"We have continued to see signs of possibly more ballistic missile launches. We also forecast North Korea could fire an intercontinental ballistic missile," Jang Kyoung-soo, acting deputy minister of national defence policy, told a parliament hearing on Monday.
North Korea tested two ICBMs in July that could fly about 10,000 km, putting many parts of the US mainland within range and prompting a new round of tough international sanctions.
South Korea's air force and army conducted exercises involving long-range air- to-surface and ballistic missiles on Monday following the North's nuclear test on Sunday, its joint chiefs of staff said in a statement.
In addition to the drill, South Korea will cooperate with the United States and seek to deploy "strategic assets like aircraft carriers and strategic bombers", Jang said.
Japanese and South Korean stock markets both closed down about 1 per cent on Monday, while safe-haven assets including gold and sovereign bonds ticked higher, but trade was cautious. US stock markets were closed for the Labor Day holiday.
US Correspondent Nick Harper spoke to Duncan Garner.
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