"The United States supports creating two permanent seats for Africa on the council," Thomas-Greenfield said during a Council on Foreign Relations (CFR) forum.
Thomas-Greenfield said that the current system of non-permanent seats limits African nations from fully contributing to the UNSC's work.
"The United States supports creating a new elected seat on the Security Council for small island developing states," Thomas-Greenfield added.
Last month, UN Secretary-General Antonio Guterres said that the UN Security Council needs a "permanent voice" for Africa among its ranks. Guterres called it unacceptable that the body in charge of the world's security "lacks a permanent voice for a continent of well over a billion people," which makes up 28% of the membership of the United Nations.
However, Russian Deputy Ambassador to the United Nations Dmitry Polyanskiy said that to preserve the UN Security Council's authority, its membership must remain limited. He further explained that a UN Security Council with 25 to 30 members would struggle to function effectively.