The United States announced on Friday that it will send Ukraine cluster munitions - prohibited by more than 100 countries - as part of an $800 million security package, a move Ukraine said would have an "extraordinary psycho-emotional impact" on Russian forces.

Jake Sullivan, President Joe Biden's national security adviser, sought to make the case for providing these arms to Ukraine shortly before the Pentagon formally announced the aid. Cluster munitions could boost Ukraine's counteroffensive to reclaim territory seized since Russia invaded in February 2022.

The decision comes on the eve of the NATO summit in Lithuania, where President Joe Biden is likely to face questions from allies on why the U.S. would send a weapon into Ukraine that more than two-thirds of alliance members have banned because it has a track record for causing many civilian casualties. And it was met with divided reactions from Congress, as some Democrats criticized the plan while some Republicans backed it.

The munitions — which are bombs that open in the air and release scores of smaller bomblets — are seen by the U.S. as a way to get Kyiv critically needed ammunition to help bolster its offensive and push through Russian front lines. U.S. leaders debated the thorny issue for months, before Biden made the final decision this week.