The United States is tracking a North Korean-flagged freighter that could be carrying weapons to an unknown destination, a U.S. official said Friday.

A defense official told FOX News the ship will most likely not be stopped at sea because the exact nature of the payload is not known.

However, the official said that would change if "we find out it is carrying ballistic missiles to a bad guy."

The payload would also be searched if the ship, which is being tracked by U.S. satellites, pulls into a port of a country that is taking part in the Proliferation Security Initiative, the official said on the condition of anonymity.

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The vessel was believed to have left North Korea sometime in the past week, in the time since the United Nations imposed sanctions against Pyongyang for its Oct. 9 underground nuclear test.

U.S. officials said suspicious vessels are frequently tracked on the high seas, but this is believed to be the first time that a North Korean ship that could be carrying an embargoed payload has been monitored since the sanctions were imposed.

The issue has taken on added importance in light of the North's nuclear test, as U.S. officials have said that Pyongyang has never had a weapons system that it was not willing to sell.