Britain is to cut its global aid budget by £2.9bn this year due to the economic impact of the coronavirus crisis, the government has announced.
It said a review of aid projects has prioritised the most vulnerable countries for assistance.
Foreign Secretary Dominic Raab said the UK would still meet its commitment to spend 0.7% of gross national income (GNI) on international development.
But MPs criticised the announcement's timing as Parliament breaks for summer.
Labour MP Sarah Champion, chairwoman of the Commons International Development Committee, said it was "poor practice" to announce the move on the final day of Parliament before the summer, preventing MPs from asking questions about it.
In a letter to Ms Champion, Mr Raab said the UK was "experiencing a severe economic downturn as a result of the Covid-19 pandemic".
Despite the reductions, Mr Raab said money spent this year "remains prioritised on poverty reduction".
He added that aid would also focus on "tackling climate change and reversing biodiversity loss, championing girls' education, UK leadership in the global response to Covid-19, and campaigning on issues such as media freedom and freedom of religious belief".
Spending on Official Development Assistance (ODA) was set to be £15.8bn this year, before the Covid-19 crisis emerged.
Mr Raab said spending on ODA would remain at 0.7% of GNI.
The foreign secretary suggested the cuts were in anticipation of "potential shrinkage" in the UK economy in the coming months.
He said a £2.9bn package of reductions in the government's planned foreign aid spending had been identified "so we can proceed prudently for the remainder of 2020".
"The package I have agreed with the prime minister maintains our flexibility and enables the government to manage our ODA spend against an uncertain 0.7% position," he added.
It comes after Prime Minister Boris Johnson announced the Department for International Development (DFID) would be merged with Mr Raab's department.
The PM said at the time that UK aid spending had "been treated as some giant cashpoint in the sky that arrives without any reference to UK interests".
Ms Champion said Mr Raab's announcement on the last day of Parliament before the long summer recess raises more questions than it answers" and queried the timescale of the cuts.
"If it is with immediate effect, do the projects know or will they find out via the media as DFID staff did about the merger? Is there an overarching strategy in place?" she wrote.
She added: "Clearly there has been no consultation, but to release this news literally as Parliament rises so there can be no scrutiny by MPs is poor practice."
Liberal Democrat international development spokesperson Wendy Chamberlain said assurances over foreign aid were not "worth the paper they were written on".