North Korea's botched missile test may have been disrupted by a secretive US programme of cyber and electronic warfare designed to sabotage launches.
The attempted test, and a weekend parade of Pyongyang's military hardware, prompted international condemnation and an American promise of further action if the hermit state failed to end its provocations.
It came as the US's national security adviser confirmed for the first time that Washington was working with China to rein in North Korea's nuclear weapons programme.
Pyongyang spent the weekend showing off its arsenal of ballistic missiles alongside thousands of goose-stepping troops in a military parade.
But the regime suffered a humiliating setback when a test-launched medium-range missile exploded four to five seconds into its flight. Its destruction raised immediate suspicions that it had fallen victim to sabotage.
"It could have failed because the system is not competent enough to make it work, but there is a very strong belief that the US - through cyber methods - has been successful on several occasions in interrupting these sorts of tests and making them fail," Sir Malcolm Rifkind, a former UK Conservative Foreign Secretary, told the BBC.
Under President Barack Obama, the US stepped up electronic and cyber attacks on North Korea's missile programme.
Those efforts are reported to include hacking and the use of electromagnetic weapons capable of disrupting electronic equipment.
Despite the new failure, the US fears the country's erratic leader, Kim Jong Un, could soon have a missile capable of reaching the American mainland.
Donald Trump's national security adviser promised further action to ensure North Korea was never able to threaten the United States.
Lieutenant General H R McMaster said the US was working with partners to tackle Kim's provocative and destabilising behaviour.
"While it's unclear and we do not want to telegraph in any way how we'll respond to certain incidents, it's clear that the president is determined not to allow this kind of capability to threaten the United States," he told ABC News
He said the test was the latest example of Pyongyang's threatening behaviour and confirmed for the first time that the US was working with China to tackle the danger.
"There is an international consensus now, including the Chinese leadership, that this is a situation that just cannot continue," he said.
Tensions remain high despite the failure. North Korea is believed to be preparing for its sixth test of a nuclear weapon in 10 years and analysts have been poring over images of the weapons displayed in Saturday's parade, including what might be a new generation of ballistic missile eventually capable of striking the US.
When he took office, Trump was warned by his predecessor that North Korea would be his stiffest challenge and the White House recently completely a review of its strategy, which officials described as "maximum pressure and engagement".
As well as a more muscular military position, the Administration is working with China to increase economic pressure on Pyongyang. Trump took to Twitter to defend what critics see as a softening of his attitude to Beijing.
"Why would I call China a currency manipulator when they are working with us on the North Korean problem? We will see what happens," he wrote.
The diplomatic and military manoeuvring continues.
A US fleet, headed by the USS Carl Vinson, is approaching the Korean Peninsula and Mike Pence, the US Vice-President, arrived in Seoul for talks with South Korea.