Israel has given retired U.S.-supplied Cobra combat helicopters to Jordan to help the Hashemite kingdom fend off insurgent threats on the Syrian and Iraqi borders, a U.S. official with knowledge of the deal said.

The handover, initiated last year, was approved by Washington, which provided mechanical overhauls for the aircraft before they were incorporated free of charge in Jordan's existing Cobra fleet, the official said.

"These choppers are for border security," the official, who requested anonymity due to the sensitivity of the issue, told Reuters.

Asked how many Cobras were transferred, the official said: "Around 16, though some may have been used by the Jordanians for spare parts" rather than kept intact.

Jordanian and Israeli officials declined comment, as did the Pentagon.