People watch a television screen showing a news broadcast with file footage of a North Korean missile launch, at a railway station in Seoul, April 2. Yonhap

North Korea fired what appeared to be an intermediate-range ballistic missile (IRBM) into the East Sea on Tuesday, the South Korean military said, in its third ballistic missile launch of the year.

The Joint Chiefs of Staff (JCS) said in a message to reporters that it detected a missile presumed to be intermediate-range class fired from the Pyongyang region at 6:53 a.m. and the missile flew about 600 kilometers before landing in the East Sea.

Military officials suspect the North may have test-fired an intermediate-range missile equipped with a hypersonic warhead to test the performance of its delivery system following an engine test last month.

On March 20, Pyongyang said it successfully conducted a ground jet test of a solid-fuel engine for a new type of intermediate hypersonic missile.

"North Korea appears to have put a hypersonic warhead on top of the delivery system used in the engine test last month," a senior military official said on the background.

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Although the North Korean missile flew for less than 10 minutes, shorter than the flight time of past IRBM launches, its speed was similar to that of a hypersonic missile, the official said.

"(We) assess the (latest launch) is connected to the solid-fuel ground test that North Korea made public in March," Col. Lee Sung-jun, spokesperson for the JCS, said in a regular briefing.

Hypersonic missiles travel at a speed of at least Mach 5 — five times the speed of sound — and are designed to be maneuverable on unpredictable flight paths and fly at low altitudes. At Mach 5 or higher, such a missile can travel the 195 kilometers between Pyongyang and Seoul in just one to two minutes.

Tuesday's launch marks North Korea's third ballistic missile launch this year.

On Jan. 14, the North test-fired a solid-fuel intermediate-range ballistic missile carrying a hypersonic warhead. Last month, North Korean leader Kim Jong-un guided firing drills involving super-large multiple rocket launchers that are also considered a ballistic missile system.

When asked about the possible differences between the latest launch and the January one, Lee said there were similarities as well as differences without offering details, noting that further analysis was required.

"There is a possibility that the launch vehicle's capabilities have been enhanced," he said.

The South Korean military denounced the North's latest missile launch as a "provocative act" and vowed to step up military vigilance against possible signs of provocations.

"While strengthening our monitoring and vigilance, our military has been closely coordinating with the United States to monitor additional signs of North Korea's provocations," the JCS said.

The South Korean military has been closely monitoring North Korea's preparations for potential weapons tests and a spy satellite launch ahead of the April 10 parliamentary elections and major political events in Pyongyang this month.

North Korea's two major holidays in April are the birthday of the country's founder, Kim Il-sung, the late grandfather of leader Kim Jong-un, on April 15 and the founding anniversary of the Korean People's Revolutionary Army on April 25. (Yonhap)