North Korea said it had successfully launched ballistic missiles from a train for the first time and was continuing to bolster its defences, after the two Koreas test-fired missiles hours apart in duelling displays of military might.

Wednesday’s launches underscored a return of the tensions between the rivals amid a prolonged stalemate in US-led talks aimed at stripping North Korea of its nuclear weapons programme.

Pyongyang’s official Korean Central News Agency said Thursday’s missiles were launched during a drill of a “railway-borne missile regiment” that transported the weapons system along rail tracks in the country’s mountainous central region and accurately struck a sea target 500 miles (800km) away.

State media showed what appeared to be two different missiles streaking up from rail-car launchers engulfed in orange flames along tracks surrounded by dense forest.

A rail-based ballistic system reflects North Korea’s efforts to diversify its launch options, which now includes various vehicles and ground launch pads and may eventually include submarines.

Firing a missile from a train could add mobility, but some experts say North Korea’s simple rail networks running through its relatively small territory would be quickly destroyed by enemies during a crisis.

“Our military assesses that North Korea is continuously developing various mobile launch equipment,” Colonel Kim Jun-rak, a spokesman for South Korea’s Joint Chiefs of Staff, said.

He said the South Korean and US militaries were continuing to examine the North’s launches.

The South Korean and Japanese militaries said earlier that North Korea’s two short-range ballistic missiles had landed inside Japan’s exclusive economic zone but outside its territorial waters on Wednesday.

The last time a North Korean missile landed inside that zone was in October 2019.

Pak Jong Chon, a senior North Korean official who has been seen as influential in the country’s missile development, said Wednesday’s tests were successfully conducted in line with the “strategic and tactical design and intention” of the North’s ruling Workers’ Party.

North Korean leader Kim Jong Un vowed at a party congress in January to bolster his nuclear deterrent in the face of US-led sanctions and pressure and issued a long wish list of sophisticated weaponry, including longer-range intercontinental ballistic missiles, nuclear-powered submarines, spy satellites and tactical nuclear arms.

In another weapons display over the weekend, the North said it tested new cruise missiles – which it intended to make nuclear-capable – that could strike targets 932 miles (1,500km) away, a distance putting all of Japan and US military installations there within reach.

Hours after the North Korean launches on Wednesday, South Korea reported its first test of a submarine-launched ballistic missile.

South Korea, which does not have nuclear weapons and is instead protected by America’s, has been accelerating efforts to build up its conventional arms, including developing more powerful missiles.