The government is reportedly planning to cut hundreds of millions of pounds from foreign aid given to countries in conflict zones.
A leaked document obtained by openDemocracy said civil servants had discussed reducing aid to Syria from £137m pledged last year to just over £45m this year.
It added that in South Sudan, spending could drop from £110m to £45m, while aid to Libya could be cut by 63% and Somalia by 60%.
The Foreign and Commonwealth Office (FCO) did not dispute the reported figures when asked by Sky News for a response, and said COVID-19 had "forced" it to take "tough but necessary decisions".
It said it was "temporarily reducing the overall amount we spend on aid".
The move has been criticised by politicians and charities, with some warning "people will die".
They say there will be huge impacts on issues such as terrorism, migration and refugee crises.
Labour's Preet Kaur Gill, shadow secretary for international development, said: "This is a devastating reminder of the real world impact the government's politically motivated decision to abandon its manifesto commitment on aid will have on the world's most vulnerable people.
"Cuts in support to countries in the midst of multiple humanitarian crises would cause devastation, leading some of the world's most vulnerable people to starve, stretched healthcare systems to collapse and access to clean water stripped away. Make no mistake, people will die."
Tory MP and chair of the House of Commons Defence Select Committee Tobias Ellwood also joined the criticism, telling Channel 4 News that terrorist groups such as Islamic State and Boko Haram will benefit from the UK stepping back.
"Perhaps we should explain it to the British people that extremism, terrorism, refugee crises, migration... will all be affected when we take these retrograde steps," he said.
Meanwhile, more than 100 charities have condemned the decision to cut aid to Yemen.
The UK has pledged at least £87m in aid, down from £160m in 2020 and £200m in 2019.
In a letter to Boris Johnson, the charities said the cuts are taking place with "no transparency, consultation or meaningful strategy".
"History will not judge this nation kindly if the government chooses to step away from the people in Yemen and thus destroy the UK's global reputation as a country that steps up to help those most in need," they said.
The FCO said: "We are still working through what this means for individual programmes and decisions have not yet been made.
"We remain a world-leading aid donor and we will spend more than £10bn this year to fight poverty, tackle climate change and improve global health."
