President Donald Trump has directed the Pentagon to prepare plans for carrying out his threat to "take back" the Panama Canal, including by military force if needed, two U.S. officials familiar with the situation told NBC News Thursday.

Potential plans range from partnering more closely with Panamanian security forces to a less likely option of U.S. troops' seizing the canal by force, U.S. officials told NBC News.

Donald Trump has said repeatedly that he wants to “take back” the Panama Canal but has not offered specifics about how he would do so. Here is an explanation of the history and laws governing the critical waterway.