FACTBOX: North Korea's missile arsenal

Former U.S. President Bill Clinton arrived in North Korea on Tuesday to try to negotiate the release of two U.S. journalists convicted by the communist state of "grave crimes," South Korea's Yonhap news agency said.

U.S. officials fear that North Korea might try to use the journalists as leverage in trying to resist international pressure to halt its arms program and weather U.N. sanctions over its missile and nuclear tests.

Following is a look at the North's missile program:

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