The latest launches came just hours after Pyongyang warned of a "stronger and certain" reaction to the sanctions on five North Koreans linked to the country's ballistic missile programme.

Seoul's Joint Chiefs of Staff said it had detected two short-range ballistic missiles fired from North Pyongan province, adding they were "analysing the specifications".

The weapons likely "fell outside" Japan's territorial waters, Tokyo's Defence Minister Nobuo Kishi told reporters, adding that the repeated tests indicated Pyongyang was "aiming to improve its launch technology".

The Friday missiles came hours after Pyongyang accused the US of "provocation" over fresh sanctions imposed this week in response to a recent string of weapons tests.

The launches were at 2.41 pm and 2.52 pm (0541 GMT and 0552 GMT), with the weapons flying a distance of 430 kilometres at an altitude of 36 kilometres, according to Seoul's Joint Chiefs of Staff.

Seoul's National Security Council expressed "strong regret" over the recent missile launches, saying they "do not contribute to stability on the Korean Peninsula at this important juncture."

Pyongyang debuted a hypersonic missile in September last year, and carried out what it called two successful tests this month, as it looks to add the sophisticated weapon to its arsenal.

In response, the United States imposed new sanctions on Pyongyang this week, with Secretary of State Antony Blinken saying North Korea was likely "trying to get attention" with the missile launches.

Pyongyang accused the United States of "intentionally escalating" the situation, saying it had a "legitimate right" to self-defence, a foreign ministry spokesman told state media.

If "the US adopts such a confrontational stance, the DPRK will be forced to take stronger and certain reaction to it," the spokesman said in comments carried by state news agency KCNA early Friday.

The timing and location of the Friday launch indicated it was a response to the US sanctions, analysts said.

"It was carried out in a rush to signal to the US that it will be a tit-for-tat on sanctions," said Cheong Seong-chang, director of the Center for North Korea Studies at the Sejong Institute.

Leif-Eric Easley, a professor at Ewha Womans University in Seoul said North Korea was trying to "lay a trap" for the US.

"It has queued up missiles that it wants to test anyway and is responding to US pressure with additional provocations in an effort to extort concessions," he said.

- Refused to talk -

Yang Moo-jin, a professor at the University of North Korean Studies, said Pyongyang was sending a clear message:

"North Korea is not going to give up anything when it comes to its weaponry despite the newly imposed sanctions."

Pyongyang has refused to respond to US appeals for talks.

At a key meeting of North Korea's ruling party last month, Kim vowed to continue building up the country's defence capabilities, without mentioning the United States.

Dialogue between Washington and Pyongyang remains stalled, and impoverished North Korea is also under a rigid self-imposed coronavirus blockade that has hammered its economy.

These domestic economic problems, and the widespread suffering they are likely causing, could also be a factor motivating Pyongyang's increasingly aggressive stance.

"Pyongyang may think it's actually beneficial for them to raise tensions on the peninsula... to keep their people loyal to the regime," defector-turned-researcher Ahn Chan-il told AFP.