The $2bn (£1.5bn) of aid the US pledged this week may have been hailed as “bold and ambitious” by the UN but could be the “nail in the coffin” in changing to a shrunken, less flexible aid system dominated by Washington’s political priorities, aid experts fear.

After a year of deep cuts in aid budgets by the US and European countries, the announcement of new money for the humanitarian system is a source of some relief, but experts are deeply concerned about demands that the US has imposed on how the money should be managed and where it can go.

When the US state department announced the pledge on Tuesday, it said the UN must “adapt, shrink or die” by implementing changes and eliminating waste, and demanded that the money be funnelled through a pooled fund under the UN’s Office for the Coordination of Humanitarian Affairs (Ocha) rather than to individual agencies.

It also stipulated that the money be used for 17 priority countries chosen by the US, excluding some undergoing profound humanitarian crises such as Afghanistan and Yemen.

Themrise Khan, an independent researcher on aid systems, said: “It’s a despicable way of looking at humanitarianism and humanitarian aid.”