UNITED NATIONS (AP) — The Security Council backed reforms Wednesday to reduce inefficiencies, corruption and abuse in the U.N.'s far-flung peacekeeping operations, a key priority of the Trump administration at the U.N. General Assembly.

Vice President Mike Pence cast the approval vote for the United States, saying the U.N. must be more aggressive in evaluating the effectiveness of its operations. He said all peacekeeping missions must be deployed in support of a political solution to conflicts and have exit strategies.

"In short, when a mission succeeds, we must not prolong it. When a mission underperforms, we should restructure it. And when a mission consistently fails to fulfill a mandate of this council, we should end it," Pence said.

While many peacekeeping missions have been hailed as successful — Sierra Leone most recently — others have been criticized for sexual abuse violations and corruption, especially in the Central African Republic and Congo. The joint U.N.-African Union mission in Sudan's Darfur region has been widely criticized for inefficiency.

An Associated Press investigative series on the U.N's peacekeeping crisis uncovered roughly 2,000 allegations of sexual abuse and exploitation against peacekeepers and other U.N. personnel during a 12-year period. It found that the U.N. often lost track of the victims and that only a fraction of the perpetrators were held accountable.

Adding to the challenges is the changing nature of conflicts around the world. Often the main players are rebel groups and fighters who act outside of international law, rather than conflicts between different countries. As a result, U.N. peacekeepers have increasingly been killed, injured or kidnapped.

The Security Council asked for annual briefings from U.N. Secretary-General Antonio Guterres on his initiative to reform peacekeeping.

Guterres shares U.S. concerns that peacekeeping missions often get bogged down in ever-evolving conflicts without sufficient resources or an adequate political strategy.

But the Trump administration stoked alarm in the U.N. with a proposal to cut U.S. funding for U.N. peacekeeping by $1.3 billion, over 50 percent. The United States currently pays 28.57 percent of the peacekeeping budget, nearly triple the second-largest contributor, China.

U.N. officials have pushed back on the idea that its peacekeeping operations are not cost-efficient. Guterres pointed to 55 operations that have wrapped up over the years, achieving peace in countries around the world.

There are currently 16 U.N. peacekeeping operations under way, with more than 100,000 personnel, at an annual cost of nearly $8 billion. The U.N. has said that, adjusted for inflation, the cost to member states has decreased by 17 percent in the past decade by one measure. Three missions — Haiti, Ivory Coast and Liberia — are scheduled to end by March 2018, which will save hundreds of millions of dollars.

"Peacekeeping remains a highly cost-effect instrument," Guterres told the council.

Still, he outlined plans for reform with four goals in mind.

The first, he said, is ensuring that "peace operations are deployed in support of active diplomatic efforts, not as a substitute." To that end, Guterres has changed the structure of the U.N. secretariat to consolidate the management of both peacekeeping operations and large political missions.

The second challenge is ensuring that peacekeepers are properly equipped. Guterres said there are critical gaps in technology, transportation, intelligence and other capabilities. The Security Council resolution called on member states to fulfill pledges to provide those capabilities and asked Guterres to provide a report within 90 days on a mechanism to fill the gaps.

The third goal is to stamp out corruption and abuses that have tarnished the reputation of U.N. peacekeeping, particularly sex abuse scandals.

Guterres said he has taken "strong steps" to fight the problem, which he says has haunted him. He pointed in particular to the appointment of a victims' rights advocate and a requirement that member states certify prior to deployment that none of their personnel has a history of misconduct.

However, a major challenge is that the U.N. lacks legal jurisdiction over its peacekeeping force and relies on member states to prosecute crimes by their own troops, making justice elusive in many cases.

The Security Council was divided over a fourth goal, that of strengthening partnerships with regional entities, especially the African Union, which has taken the helm of various peacekeeping operations.

Council members disagreed on whether to help finance AU operations on a case-by-case basis with U.N. contributions. In the end, the Security Council resolved to consider steps toward establishing a mechanism through which AU operations could be partly financed by the U.N.