The Norwegian Refugee Council, one of the world's biggest aid agencies, announced that it was "forced" to suspend some of its humanitarian activities in almost 20 countries due to the US aid freeze under President Donald Trump.
The non-governmental organisation received just under 20% of its funding from the United States in 2024, or around $150 million, it said, with that funding helping some 1.6 million people worldwide.
"We have, in our 79-year history, never experienced such an abrupt discontinuation of aid funding from any of our many donor nations, inter-governmental organisations, or private donor agencies," the NRC said in a statement.
The agency said the consequences of suspending aid would become increasingly serious for people facing crises around the world.
It comes as the Roman Catholic Church's worldwide charity arm sharply criticised the cuts, saying Mr Trump's plans to end funding for relief agency USAID will have a "catastrophic" impact in the developing world.
"The ruthless and chaotic way this callous decision is being implemented threatens the lives and dignity of millions," Caritas Internationalis, a Vatican-based confederation of 162 Catholic relief, development and social services organisations working in more than 200 countries, said in a statement.
A number of these groups received money from USAID and other US government funds for various international programmes.
The US Agency for International Development (USAID) is Washington's primary humanitarian aid agency.
It has been a top target of a government reduction programme spearheaded by billionaire and Trump ally Elon Musk since the Republican president took office on 20 January.
The Trump administration said on Friday it would keep 611 essential workers on board at the agency, out of a worldwide total of more than 10,000 employees, but a federal judge temporarily blocked some of the layoffs.
Last month, the US State Department issued a "stop-work" order for all existing foreign assistance programmes.
In the 2023 fiscal year, the United States disbursed, partly via USAID, $72bn of aid worldwide.
In its statement, Caritas said the cuts would "kill millions of people and condemn hundreds of millions more to lives of dehumanising poverty". The cuts will make the agency "completely reassess whom we can continue to serve and how," it said.
Other Catholic charity agencies are also known to be reassessing their global aid efforts.
US-based Catholic Relief Services, which has about 5,000 employees, told staffers last week to expect layoffs because of the US administration's cuts to their foreign aid grants.
The organisation has a $1.5 billion budget, about half funded by USAID.
The US Conference of Catholic Bishops has also laid off 50 staffers at its national office in Washington, because of cuts to federal grants for work on migration and refugee resettlement issues.
Pope Francis himself has not commented on the aid cuts, but has been sharply critical of some of Mr Trump's priorities, such as plans to deport millions of migrants, which he has called a "disgrace".
