Libyan government fighters discovered a cache of powerful American missiles, usually sold only to close American allies, at a captured rebel base in the mountains south of Tripoli this week.

The four Javelin anti-tank missiles, which cost more than $170,000 each, had ended up bolstering the arsenal of Gen. Khalifa Hifter, whose forces are waging a military campaign to take over Libya and overthrow a government the United States supports.

Markings on the missiles’ shipping containers indicate that they were originally sold to the United Arab Emirates, an important American partner, in 2008.