WASHINGTON—The Pentagon is planning to bolster the Trump administration’s new approach in Afghanistan by reallocating drones and other hardware while sending in around 1,000 new combat advisers, U.S. and military officials said.

The idea is to bulk up the U.S. military presence in Afghanistan by the time the traditional fighting season begins in the spring. The military will send a larger number of drones, both armed and unarmed, to Afghanistan for air support as well as for intelligence, surveillance and reconnaissance.

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