SEOUL, South Korea — Beyond the usual, lofty propaganda, North Korea’s test of a new intermediate-range ballistic missile contains an important, potentially worrying development.

The country’s jubilant young dictator, Kim Jong Un, said the missile provides the country with another nuclear attack capability.

Sunday’s launch — the first major North Korean challenge for U.S. President Donald Trump — is drawing intense scrutiny from outside weapons experts because of North Korea’s claim to have used solid fuel.

If true, it would be a big step forward in North Korea’s quest to boost its ability to attack the United States and its close allies, South Korea and Japan. Instead of relying on missiles that have to be fueled on a fixed launch pad, North Korea’s military could drive the new missiles anywhere and fire them at will from mobile launchers.

Here’s a look at Sunday’s launch and what it means for security on an already tense Korean Peninsula.

“Modern fuel”

The fuel in solid-fuel rockets is already loaded inside, which can shorten launch preparation times, increase the weapon’s mobility and make it harder for outsiders to detect what’s happening before liftoff.

Most of North Korea’s missiles currently use liquid propellant, which usually needs to be added on a launch pad before the weapon is fired. The rockets North Korea has used for satellite launches in recent years, which were condemned by the U.N. as tests of banned long-range missile technology, relied on liquid fuel.

“Liquid fuel is like a technology from the 1960s and ‘70s, while solid fuel is a modern fuel for missiles,” said Lee Choon Geun, an analyst from South Korea’s state-funded Science and Technology Policy Institute. “That’s why we think their latest launch (with solid fuel) is a serious development.”

Before Sunday’s test, analysts thought North Korea’s solid-fuel weapons were limited to a submarine-launched ballistic missile that the country test-fired last August and short-range KN-02 missiles.

This latest test is important because, if confirmed, North Korea would have a missile that could be launched anywhere from a ground-based mobile vehicle. While submarines are also a stealthy way to do that, North Korea doesn’t have enough of them. There are doubts that the KN-02 missile, whose range is about 120 kilometers (75 miles), can carry nuclear warheads.