Kim Jong Un
North Korean leader Kim Jong Un inspects the construction site of Ryomyong Street, in this undated photo released by North Korea's Korean Central News Agency (KCNA), Jan. 26, 2017. KCNA via REUTERS

North Korea is continuing its preparations for the next nuclear test, according to satellite images released Thursday by 38 North, a website run by the U.S.-Korea Institute at Johns Hopkins University in Washington. This follows Pyongyang’s launches of four ballistic missiles earlier this week, triggering international condemnation.

The satellite images of North Korea’s Punggye-ri test site were taken Tuesday. According to an analysis provided by 38 North, the reclusive country is continuing activities at the North Portal, the main administrative area and the command center of the site.

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“The sum of these activities supports an assessment that North Korea continues to prepare the tunnels at the North Portal for a future nuclear test. It also suggests that Punggye-ri is capable of handling a sixth nuclear test on short notice once a nuclear device and the associated monitoring equipment are emplaced. However, it is not possible to predict the timing of such a test based on the latest image,” 38 North reported.

In the North Portal, the equipment and supplies that were present last month have been replaced by what appears to be a large shipping container or crate. And at the main administrative area, a 5-meter truck and supplies in the northern courtyard, which were seen in February, are not present, the report added.

On Tuesday, North Korea said the ballistic missile launches were a part of drills targeting U.S. military bases in Japan. The missiles, which were launched from the Dongchang-ri long-range missile site in North Pyongan Province, flew about 620 miles before splashing into the Sea of Japan.

The country’s leader Kim Jong Un reportedly ordered the Korean People’s Army Strategic Force to be on high alert for any war and “get fully ready to promptly move, take positions and strike so that it can open fire to annihilate the enemies once the Party Central Committee issues an order.”

Pyongyang is not allowed to test any ballistic missile technology under a set of U.N. resolutions.