North Korea test-fired a new type of short-range ballistic missile, a U.S. official who reviewed the latest intelligence assessment of the launch told Fox News on Thursday.

The first missile flew 270 miles early Thursday morning local time, but the second missile fired off about 30 minutes later is the one officials are most concerned about. It flew roughly 430 miles putting all of South Korea in range.

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“It’s like putting a V8 engine on a V6,” said the official, who was not authorized to discuss the intelligence assessment and requested anonymity to discuss the missile launches, the first by the rogue communist regime since early May, and the first since President Trump met North Korean leader Kim Jong Un at the DMZ last month.

The official said the new North Korean short-range missiles are similar to the ones fired off in May, but the missiles launched early this morning from the east coast town of Wonsan appear more powerful.

The missile launches come two days after Kim Jong Un was photographed at a North Korean shipyard where a new type of ballistic-missile carrying submarine is being constructed, according to Korean Central News Agency (KCNA), the communist government’s propaganda arm.

U.S. officials say it’s not immediately clear if this new type of ballistic missile test-fired from a mobile launcher could be modified to fit on the submarine to be able to launch from under the sea in the future.

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The launch took place as Trump’s national security adviser John Bolton wrapped up a visit to Seoul, South Korea, the Kim regime called Bolton a “warmonger” and “human defect” following comments he made in May after North Kora’s last missile test, which officials said were based on a Russian design.

Earlier this week, a pair of Russian long-range nuclear-capable bombers joined Chinese bombers for joint operations for the first time in the skies near South Korea.

A Russian A-50 airborne warning and control plane broke off from the formation and flew into South Korean air space, according to South Korean officials who launched alert fighter jets. After ignoring repeated radio calls to vacate the area, the South Korean fighters jets fired 360 warning shots near the Russian airborne radar plane. The Russian government says it is investigating the incident.

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Trump will speak at the Pentagon Thursday morning at a ceremony to honor his new defense secretary, Mark Esper, overwhelmingly confirmed by the Senate 90-8 Tuesday.

The Pentagon had not had a Senate-confirmed defense chief since Jim Mattis resigned in December.