SEOUL, South Korea — North Korea on Friday bragged of its recently tested new intercontinental ballistic missile, calling it “the world’s strongest,” a claim viewed by outside experts as propaganda though the test showed an advancement in the North’s quest to build a more reliable weapons arsenal.

A missile launched by North Korea on Thursday flew higher and stayed in the air for a longer duration than any other weapon the country had so far fired. It signaled that the North has achieved progress in acquiring a nuclear-armed ICBM that can hit the U.S. mainland. But foreign experts assess that the country has still a few remaining technological issues to master before acquiring such a functioning ICBM.

On Friday, the North’s Korean Central News Agency identified the missile as the “Hwasong-19” ICBM and called it “the world’s strongest strategic missile” and “the perfected weapon system.”

KCNA said leader Kim Jong Un observed the launch, describing it as “an appropriate military action” to express North Korea’s resolve to respond to its enemies’ moves that escalated tensions and threats to North Korea’s national security. It said Kim thanked weapons scientists for demonstrating North Korea’s “matchless strategic nuclear attack capability.”

South Korea’s military earlier said that North Korea could have tested a solid-fueled missile, but Friday’s KCNA dispatch did not say what propellant the Hwasong-19 ICBM uses. Observers say the color of exhaust flames seen in North Korean media photos on the launch still suggest the new ICBM uses solid fuels.

Before Thursday’s test, North Korea’s most advanced ICBM was known as the “Hwasong-18” missile, which uses solid fuels. Pre-loaded solid propellants make it easier to move missiles and require much less launch preparation time than liquid propellants that must be fueled before liftoffs. So it’s more difficult for opponents to detect launches by solid-fuel missiles.

In recent years, North Korea has reported steady advancement in its efforts to obtain nuclear-tipped missiles. Many foreign experts believe North Korea most likely has missiles that can deliver nuclear strikes on all of South Korea, but it has yet to possess nuclear missiles that can travel to the mainland U.S.

There are questions on whether North Korea has acquired the technology to shield warheads from the high-temperature, high-stress environment of atmospheric reentry. Many foreign analysts say North Korea also must have improved altitude control and guidance systems for missiles. They say North Korea needs an ability to place multiple warheads on a single missile to defeat its rivals’ missile defenses.

All of North Korea’s known ICBM tests, including Thursday’s, have been performed on steep angles to avoid neighboring countries. South Korean military spokesperson Lee Sung Joon said Thursday that a high-angle trajectory launch cannot verify a missile’s re-entry vehicle technology, though North Korea has previously claimed to have acquired that technology.

Observers say that Thursday’s launch, the North’s first ICBM test in almost a year, was largely meant to grab American attention days before the U.S. presidential election and respond to international condemnation over North Korea’s reported dispatch of troops to Russia to support its war against Ukraine.

North Korea’s reported troop dispatch highlights the expanding military cooperation between North Korea and Russia. South Korea, the U.S. and others worry that North Korea might seek high-tech, sensitive Russian technology to perfect its nuclear and missile programs in return for joining the Russia-Ukraine war.