Recent satellite imagery has shown vehicle activity at a major North Korean missile site, suggesting Pyongyang may be in the early stages of preparing for a missile or missile engine test.

Citing a number of U.S. officials on Sunday, CNN reported that the vehicles were sighted at the Sanumdong missile research center near the North Korean capital.

The vehicles, however, are not believed to be involved in the fueling of missiles and officials in Washington are not certain whether Pyongyang is preparing to launch a short or medium-range missile or conduct an engine test.

Officials are not ruling out the possibility of an imminent missile test since the activities are "consistent" with what they had seen prior to previous tests.

Researchers at The Middlebury Institute cautioned that the North is well aware their sites are being monitored by American satellites and the latest activity may be part of its attempts to mislead U.S. intelligence.

Recent commercial satellite imagery captured by Planet Labs and analyzed by the Institute also showed a large blue shipping container moving about at the same location, days after North Korean leader Kim Jong-un announced he would develop new "strategic" weapons in the face of what he called Washington's "hostile policy."

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