North Korea has said the United States would "suffer the greatest pain" over its role in the imposition of the latest sanctions on the country.

His comments come after the UN Security Council unanimously adopted a US-draft resolution slapping new sanctions on North Korea.

"The forthcoming measures ... will make the US suffer the greatest pain it ever experienced in its history," Han Tae Song, North Korea's ambassador to the UN, said on Tuesday.

The resolution is a watered-down version of the original US proposal, but it does ban North Korea from importing all natural gas liquids and condensates, and bans all textile exports and prohibits all countries from authorising new work permits for North Korean workers.

Han rejected the resolution as "illegal and unlawful" and said the US was "fired up for political, economic, and military confrontation".

North Korea is "ready to use a form of ultimate means", Han said.

On Wednesday, North Korea also called the sanctions a "heinous provocation aimed at depriving the DPRK of its legitimate right for self-defence and completely suffocating its state and people through full-scale economic blockade," according to a statement from the state-run Korean Central News Agency (KCNA).

DPRK stands for North Korea's formal name, the Democratic People's Republic of Korea.

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The statement also said that the sanctions "verify that the road [North Korea] chose to go down was absolutely right and to strengthen its resolve to follow this road at a faster pace without the slightest diversion until this right to finish is over".

Monday's text is the ninth resolution unanimously adopted by the 15-member council since 2006 over North Korea's ballistic missile and nuclear programme.

It came in response to Pyongyang's sixth and largest nuclear test on September 3, which it said was of an advanced hydrogen bomb.

'Very small step'

For his part, US President Donald Trump said on Tuesday the latest UN sanctions on North Korea were only a very small step and nothing compared with what would have to happen to deal with the country's nuclear programme.

"We think it's just another very small step, not a big deal," Trump said at the start of a meeting with Malaysian Prime Minister Najib Razak.

"I don't know if it has any impact, but certainly it was nice to get a 15-to-nothing vote, but those sanctions are nothing compared to what ultimately will have to happen."

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Trump has pledged not to allow North Korea to develop a nuclear missile capable of hitting the US.

The initial US proposal included an asset freeze on North Korean leader Kim Jong-un and a complete ban on countries selling oil to his government, but the measures were softened to appease China and Russia.

Steven Mnuchin, the US treasury secretary, gave warned China that if it did not follow through on the new sanctions, the US would "put additional sanctions on them and prevent them from accessing the US and international dollar system".

Another senior administration official told Reuters news agency that any such "secondary sanctions" on Chinese banks and other companies were on hold, for now, to give China time to show it was prepared to enforce the latest and previous rounds of sanctions fully.

Frustrated US legislators called at a House hearing on Tuesday for a "supercharged" response to North Korea's nuclear and missile tests and said the US should act alone if necessary to stiffen sanctions on Chinese firms and any country doing business with North Korea.

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Ed Royce, the Republican chairman of the US House Foreign Affairs Committee, said time was running out and Chinese firms should be given "a choice between doing business with North Korea or the United States".

Marshall Billingslea, US assistant treasury secretary, acknowledged at the hearing he had not seen sufficient evidence that past sanctions were effective, but defended the administration's strategy.

He called on anyone aware of efforts to enable North Korean trade to come forward before getting caught, warning: "We are closing in on North Korea's trade representatives."

China's official Xinhua news agency said in a commentary that the Trump administration was making a mistake by rejecting diplomatic engagement with North Korea.

"The US needs to switch from isolation to communication in order to end an 'endless loop' on the Korean Peninsula, where nuclear and missile tests trigger tougher sanctions and tougher sanctions invite further tests," it said.

Liu Jieyi, China's UN ambassador, called on North Korea to "take seriously the expectations and will of the international community" that it halt its nuclear and ballistic missile development, and called on all parties to remain "cool-headed" and not stoke tensions.

Liu said relevant parties should resume negotiations "sooner rather than later".

To kick-start talks, China and Russia have proposed a dual suspension of North Korea's nuclear and ballistic missile testing, as well as US and South Korean military exercises.

The US has called the proposal insulting.