The United Nations has dispatched an envoy to North Korea for a rare visit aimed at defusing tensions over Pyongyang's intercontinental ballistic missile launch, as the US and South Korea began joint military exercises condemned by Kim Jong-Un's regime.
The unusual visit by Jeffrey Feltman, which begins Tuesday and runs to Friday, comes less than a week after North Korea test-fired a ballistic missile believed capable of reaching the United States.
On Monday, the United States and South Korea launched their biggest-ever joint air exercise -- maneuvers slammed by Pyongyang as an "all-out provocation."
The five-day Vigilant Ace drill involves 230 aircraft, including F-22 Raptor stealth jet fighters, and tens of thousands of troops, Seoul's air force said.
Pyongyang sent tensions soaring on the Korean Peninsula five days ago when it announced it had successfully test-fired a new ICBM, which it says brings the whole of the continental United States within range.
Analysts say it is unclear whether the missile survived re-entry into the earth's atmosphere or could successfully deliver a warhead to its target -- key technological hurdles for Pyongyang.
A Cathay Pacific crew spotted what was "suspected to be the re-entry" of the missile as they flew from San Francisco to Hong Kong, the airline said.
In a separate message to staff, Cathay general manager Mark Hoey said the crew described seeing the missile "blow up and fall apart," The South China Morning Post reported.
The isolated and impoverished North has staged six increasingly powerful atomic tests since 2006 -- most recently in September -- which have rattled Washington and its key regional allies South Korea and Japan.
Pyongyang faces tough international sanctions as a result of its unwillingness to surrender its nuclear and ballistic missile programs.
Ahead of his visit to Pyongyang, Feltman -- the UN under-secretary-general for political affairs -- was in Beijing on Monday. China is Pyongyang's sole diplomatic and military ally.
Once in the North, Feltman will discuss "issues of mutual interest and concern" with officials, UN spokesman Stephane Dujarric said, adding he was unable to say whether Feltman will meet with Kim.
It will be Feltman's first visit to North Korea since he took office five years ago, and the first by a UN under-secretary-general in more than seven years.
The UN envoy is planning to see foreign diplomats and UN workers in the North on humanitarian missions, Dujarric said.
In recent years, Pyongyang has accelerated its drive to bring together nuclear and missile technology capable of threatening the US, which it accuses of hostility.
US President Donald Trump has engaged in months of tit-for-tat rhetoric with Kim, pejoratively dubbing him "Little Rocket Man" and a "sick puppy."
Over the weekend, Pyongyang countered that Washington was "begging for nuclear war" as the North blasted the joint US-South Korean drills.
As well as featuring the latest generation of stealth fighters, this year's war games involve simulated precision attacks on the North's military installations, including its missile launch sites and artillery units, Yonhap news agency said, citing unnamed Seoul sources.
As tensions surged, US Senator Lindsey Graham, an influential Republican and foreign policy hawk, warned that the US was moving closer to "preemptive war" with the North.
"If there's an underground nuclear test (by the North), then you need to get ready for a very serious response by the United States," Graham told the CBS show "Face the Nation."
His remarks echoed those of Trump's National Security Adviser HR McMaster, who told a security forum on Saturday that the potential for war with the North "is increasing every day."
The North has boasted that the Hwasong 15 ICBM tested on Wednesday is capable of delivering a "super-large" nuclear warhead anywhere in the US mainland.
Analysts agree the latest test showed a big improvement in potential range, but say it was likely achieved using a dummy warhead that would have been quite light.
They say a missile carrying a much heavier nuclear warhead would struggle to travel as far.
They are also skeptical that Pyongyang has mastered the sophisticated technology required to protect such a warhead from the extreme temperatures and stresses encountered as the missile hurtles back to Earth.
The latest launch, which saw the missile drop into Japan's economic waters, was condemned Monday by Tokyo's parliament, which slammed the North's weapons program as an "imminent threat."
China's foreign ministry meanwhile warned Monday that the situation on the Korean peninsula remained "highly sensitive" and called on all sides to "do more things to ease the tension and avoid provoking each other."
The tensions have fueled concerns of another conflict, more than six decades after the 1950-53 Korean War that left much of the peninsula in ruins.
But even some Trump advisers say US military options are limited when Pyongyang could launch an artillery barrage on the South Korean capital -- only around 50 kilometers (30 miles) from the heavily-fortified border and home to 10 million people.