Washington (CNN) The Pentagon will soon issue a new policy on cluster bombs, abandoning a previous plan that mandated the military ditch older versions of the controversial weapons by 2019, according to a copy of a Defense Department memorandum signed by Deputy Secretary of Defense Patrick Shanahan and obtained by CNN.

"The Department will retain cluster munitions currently in active inventories until the capabilities they provide are replaced with enhanced and more reliable munitions," the memorandum said.

The memo called the weapons "an effective and necessary capability."

Cluster bombs -- which not only deliver an initial explosion on impact but also contain multiple smaller bombs that spread over a wide area -- are largely condemned by the international community due to the risk of civilian casualties when they're used in populated areas.

Over 100 countries, including most members of NATO, have called for a ban on the controversial weapon and human rights groups have expressed concerns over civilian casualties resulting from cluster bombs.

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