Lynsey Chutel and Farnaz Fassihi

The United States of America would support two permanent seats for African states on the U.N. Security Council, Linda Thomas-Greenfield, the American ambassador to the United Nations, said. But the path to making that promise a reality is complicated.

The announcement, which echoes a similar call from the U.N. secretary general, António Guterres, to overhaul the Council so it would reflect the world powers of the 21st century, comes ahead of the U.N. General Assembly later this month.

The Security Council has 15 members, five of which have permanent seats with veto power: the United States, Russia, China, Britain and France. The other 10 members of the Council rotate every two years. Adding any new permanent members would require the approval of all five permanent members and changing the U.N. charter, a dim prospect given the divisions among the permanent members.

Adding only African countries as permanent members would most likely get pushback from other countries, including Japan, Brazil, India, Germany and Italy. For years, those nations have also lobbied for seats, arguing that the world had evolved since the aftermath of World War II when the world body was founded.

Still, Ms. Thomas-Greenfield’s announcement could be viewed as a geopolitical gesture toward repairing U.S. relations with Africa, which have been frayed by the conflicts in Ukraine and the Gaza Strip, and toward matching Chinese and Russian influence there. The two U.S. rivals, which have been keen on expanding their influence on the continent, have already backed permanent seats for Africa on the Security Council.

Ms. Thomas-Greenfield may also be considering her legacy at the United Nations as her term possibly draws to an end, with the American election looming in November and the likelihood that a new administration would appoint a new ambassador. During her tenure, she has made Africa a priority of her diplomacy, frequently traveling to the continent.

“The problem is, these nonpermanent seats don’t enable African countries to deliver the full benefit of their knowledge and voices to the work of the Council,” Ms. Thomas-Greenfield said during a meeting at the Council on Foreign Relations, a think-tank in New York City.

The Council is tasked with maintaining peace and stability, preventing and mediating conflicts and approving U.N. peacekeeping missions, and it has the power to impose sanctions. But divisions among world powers — U.S. and European allies on one side and Russia and China on the other — has made the Council ineffective in resolving the wars in Ukraine and Gaza.

African countries have long pushed for permanent seats on the Council, arguing that the size of the population living on the continent, as well as its economy and its pressing issues, should be represented permanently at the world body. Nations from Asia, Europe and Latin America have made similar campaigns.

Africa is one of the largest voting blocs in the U.N., with 53 member states. The majority of U.N. peacekeeping missions are in Africa, and thousands of Africans serve in these missions.

Ms. Thomas-Greenfield said on Thursday that the United States would support the expansion of the Security Council’s permanent membership to include not only African members, but also a rotating seat for small island states. Her announcement, however, came with a significant catch: The White House did not back providing new permanent members with the same veto power to block resolutions that the current five permanent members have.

The issue of veto has been a thorny one because diplomats have argued that without veto power, the Council would be creating a two-tier system, with new members only symbolically present but lacking the impact or power of the other five members. At the same time, adding new veto powers would make the work of the Council even more difficult, analysts say.

The United States has also previously expressed support for adding permanent seats for Japan and Germany, two close allies.

Ms. Greenfield-Thomas’s announcement follows a Council debate last month initiated by Sierra Leone, an African country which has hosted one of the longest-running U.N. missions but has not had a voice on the Council in decades.

“Nearly 80 years after its creation, the Council has been stuck in time,” President Julius Maada Bio of Sierra Leone told its members.

Sithembile Mbete, a politics professor at the University of Pretoria who addressed the Council during that debate, said there appeared to be a growing consensus that if the Council did not change, it would be perceived as ineffective and without purpose.

“If people don’t feel like an institution is credible, then they just boycott and don’t abide by its rulings,” she said.