North Korea may be preparing for nuclear tests, as U.S. spy satellites have detected new tunnels being dug in the country, at a location where such tests have been conducted in the past, two U.S. defense officials told Fox News.

The officials said the digging indicates that another nuclear test will take place. North Korea has conducted six nuclear weapons tests in the past.

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According to the defense officials, intelligence analysts discovered excavation equipment active in Kilju, located in the Hamgyong province, at a site where a nuclear weapons test had most recently been conducted in September 2017.

An overview of what state media reports is the launch of the "Hwasong-17" intercontinental ballistic missile (ICBM) in this undated photo released on March 25, 2022, by North Korea's Korean Central News Agency (KCNA). KCNA via REUTERS

An overview of what state media reports is the launch of the "Hwasong-17" intercontinental ballistic missile (ICBM) in this undated photo released on March 25, 2022, by North Korea's Korean Central News Agency. (KCNA via REUTERS)

The news comes days after North Korea conducted its first intercontinental ballistic missile launch in four years, with North Korean leader Kim Jong Un stating he intends to develop a more powerful means of attack.

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The missile launch was North Korea's twelfth weapons test this year. It included the long-range Hwasong-17, which analysts believe is meant to reach anywhere in the mainland U.S. 

FILE - In this photo distributed by the North Korean government, North Korean leader Kim Jong Un, center, walks around what it says a Hwasong-17 intercontinental ballistic missile (ICBM) on the launcher, at an undisclosed location in North Korea on March 24, 2022. Independent journalists were not given access to cover the event depicted in this image distributed by the North Korean government. (Korean Central News Agency/Korea News Service via AP, File)

The size of the missile suggests that it is intended to carry multiple nuclear warheads. North Korea already has missiles that can carry a lone warhead and reach the much of the U.S.

North Korea Missile Launch

This photo provided by the North Korean government shows what it says a test launch of a hypersonic missile on Jan. 11, 2022 in North Korea. (Korean Central News Agency/Korea News Service via AP)

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"Only when one is equipped with the formidable striking capabilities, overwhelming military power that cannot be stopped by anyone, one can prevent a war, guarantee the security of the country and contain and put under control all threats and blackmails by the imperialists," Kim said, according to the Korean Central News Agency.

The Associated Press contributed to this report.