North Korea has conducted a successful ballistic missile test, firing a projectile into the Sea of Japan early Monday morning, CNBC and other media report, citing South Korea's Yonhap news network.

Three previous similar tests happened a week ago.

The latest missile test is at least the eighth such test this year alone. North Korea has been working on new anti-aircraft weaponry as well, according to Reuters.

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The Korea Herald reports that South Koreans scrambled in response, with South Korean President Moon Jae-in assembling an emergency meeting of the country’s security council.

The test comes during a period of heightened tensions with North Korea.

This morning, in an interview on "Face the Nation", Secretary of Defense James Mattis said a war with North Korea would be "probably the worst kind of fighting in most people's lifetime" and a "catastrophic war if this turns into a combat."