The senior policy adviser to Donald Trump has promised that the US will stand by Japan against North Korea - and said it will send the rogue state a message of 'unquestioned military strength.'

Adviser Stephen Miller said that although Trump didn't mention North Korea when he promised to 'stand by' Japan during his meeting with Prime Minister Shinzo Abe on Saturday, the speech was 'a show of strength.'

Trump would send a 'signal' after a new North Korean missile test by asking Congress to give more money to the military, Miller added in his appearance on CBS News' Face the Nation Sunday.

The government would then 'begin a great rebuilding of the armed forces of the United States,' he said, '...once again we will have unquestioned military strength beyond anything anyone can imagine.'

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Stephen Miller (pictured) said on Sunday that Donald Trump will ask Congress for money to show North Korea 'unquestioned military strength beyond anything anyone can imagine'

Miller's remark after Trump notably did not mention or condemn North Korea or its weekend launch of a new ballistic missile in his response speech with Japanese leader Abe Shinzo

That would take time, host John Dickerson noted - so would Trump be providing any more immediate response that might show the US means business?

Miller's response was to repeat that Trump's speech was 'a show of strength'.

'Saying we stand with our ally, having the two men appear on camera worldwide to all of planet Earth was a statement that will be understood very well by North Korea,' he said.

The remarks came after US Pacific Command confirmed that North Korea had launched a ballistic missile near the northwestern city of Kusong on Sunday, local time.

North Korea had warned last week that it was ready to test its first intercontinental ballistic missile.

The launch - the first during Donald Trump's time as president - prompted a short joint speech by Abe and Trump, who were at Trump's south Florida estate, Mar-a-Lago.

'North Korea's most recent missile launch is absolutely intolerable,' Abe said through a translator on Saturday night, EST.

He added that the North must comply fully with relevant UN Security Council resolutions, but also noted that Trump had assured him that the US supported Japan.

'President Trump and I myself completely share the view that we are going to promote further cooperation between the two nations. And also we are going to further reinforce our alliance,' he said.

Trump followed Abe with even fewer words, saying in part: 'I just want everybody to understand and fully know that the United States of America stands behind Japan, its great ally, 100 per cent.'

The fact that he did not directly name North Korea - nor directly condemn or denounce the launch - in the speech was noted by many.

However, it was suggested by some analysts that Trump's team had advised him to hold back on making threats that he cannot make good on.

The Obama administration had opted to stand back and slowly increase sanctions and diplomatic pressure, playing a waiting game with the Kim regime the was dubbed 'strategic patience'.

US Navy confirmed that North Korea launched the ballistic missile on Sunday, local time. Trump said he stands with Japan, but analysts say his options may be limited

By comparison, the Trump team have promised a more aggressive approach to the problem, as evidenced by Miller's comments.

But the president's options remain limited, analysts say.

A US official, speaking on condition of anonymity, said that the US wanted to shot resolve while avoiding escalation.

So direct intervention is unlikely.

Instead, the administration is likely to ramp up pressure on Beijing, which Trump has said does not do enough to rein in Pyongyang's nuclear and ballistic programs.

However, China, fearing a flood of refugees, is wary of causing destabilization in North Korea and may be hesitant to go too far.

It remains to be seen, however, whether the new administration might go a step beyond Obama's approach and focus on imposing 'secondary sanctions' on firms and entities that help North Korea's weapons programs, many of which are in China.

For now they will look at tightening financial sanctions, increasing military assets and joint exercises in and around the country, and accelerating installation of new missile defense systems in South Korea, the official said.

On Sunday morning, Trump commended Miller for his TV work.

'Congratulations Stephen Miller- on representing me this morning on the various Sunday morning shows,' he tweeted. 'Great job!'