The United Nations will be forced to reduce its peacekeeping forces worldwide by around 25 percent due to a lack of funding, largely linked to US aid cuts, a senior UN official said on Wednesday.

About 13,000 to 14,000 military and police personnel, as well as their equipment, will have to be repatriated, the official said on condition of anonymity, with "a large number of civilian staff in missions" also to be affected.

The United States was expected to contribute US$1.3 billion of the total US$5.4 billion budget for 2025-2026 peacekeeping operations.

But it has now informed the UN that it will only pay around half the amount, US$682 million – which includes US$85 million earmarked for a new international anti-gang mission in Haiti that was not in the original budget.

China is expected to contribute US$1.2 billion to the peacekeeping budget.

President Donald Trump has overseen massive cuts to US foreign aid since his return to the White House.

"We know that there will be consequences in terms of monitoring ceasefires, protection of civilians, working with the humanitarians, or other peacekeeping activities," the official said.

The 25 percent reduction in troops will be spread across the 11 missions, the official said.

The UN has peacekeepers deployed in the eastern Democratic Republic of Congo, southern Lebanon, Central African Republic, South Sudan, and Western Sahara, among other places. (AFP)