The nuclear-armed North is barred from ballistic missile tests under UN resolutions and its actions have drawn condemnation from European members of the Security Council but a comparatively sanguine response from Trump, who has met North Korean leader Kim Jong Un three times, generating global headlines on each occasion.

"I have no problem. We'll see what happens but short-range (missiles) are very standard," Trump told reporters as he left the White House for a rally in Ohio.

Kim and Trump agreed to resume denuclearisation talks during their impromptu June encounter in the Demilitarised Zone that divides the peninsula, but that working-level dialogue has yet to begin.

Pyongyang is furious over joint US-South Korean military exercises due to start next week, and analysts say the launches are intended to raise the pressure on Washington.

But the situation could also see negotiations delayed until late this year, they said.

The North fired two projectiles from its east coast in the early hours of Friday that flew around 220 kilometres (140 miles), reaching altitudes of 25 kilometres and speeds of Mach 6.9, the South's Joint Chiefs of Staff said -- unusually fast for a short-range weapon.

The flight profile was similar to Wednesday's test and Seoul's presidential office said it was highly likely to be "a new type of short-range ballistic missile".

Pyongyang described the two devices it fired earlier this week as a "newly developed large-calibre multiple launch guided rocket system".

The launches come after Pyongyang fired two devices last week that Seoul said were short-range ballistic missiles, one of them travelling almost 700 kilometres.

Kim had been "emboldened" by his DMZ handshake with Trump, said Jean Lee of the Wilson Center in Washington, and was "seeking to create a sense of urgency on the Korean Peninsula to improve his hand in anticipated nuclear negotiations".

"This is Kim's answer to Trump's claim that he's in 'no hurry' to negotiate a nuclear deal," she added.

- 'Tit-for-tat brinkmanship' -

After high tensions in 2017, when the two leaders traded personal insults and threats of war, last year saw a rapid diplomatic rapprochement on and around the peninsula.

But progress towards actual denuclearisation has been slow, with Pyongyang yet to agree to give up any of its weapons and Washington insisting the sanctions against it must remain in place.

Pyongyang has signalled the negotiations could be derailed by Washington and Seoul's refusal to scrap the annual manoeuvres between their forces, describing last week's launch as a "solemn warning to the South Korean warmongers".

Pyongyang had an "array of military platforms" it could test in response to the exercises, said Harry Kazianis of the Center for the National Interest.

"This tit-for-tat brinkmanship will clearly delay working-level talks for at least until the fall to allow both sides to save face,"  he said.

- Pixellated images -

The Pentagon has said the joint military drills will press ahead.

There are 28,500 US troops stationed in South Korea to protect it against its nuclear-armed neighbour, many of them based south of Seoul at Camp Humphreys in Pyeongtaek -- Washington's biggest overseas military facility.

On Thursday, pictures carried by the North's state television showed Kim supervising the previous day's launch from what appeared to be a mobile command post.

Pyongyang has long possessed the ability to devastate Seoul with artillery fire as it is only around 60 kilometres from the border. But a working guided rocket system capable of precision targeting would pose a new threat to installations in the South such as Camp Humphreys.

Analysts said the images appeared to show a multiple rocket launcher but some of them were heavily pixellated, indicating the North was still keeping secret some of its features.

Trump has repeatedly touted his relationship with Kim, while three UN Security Council members -- Britain, France and Germany -- have condemned Pyongyang over the spate of tests.

They urged the North to "take concrete steps towards its complete, verifiable and irreversible denuclearisation and to engage in meaningful negotiations with the US".