"Ultimately these cuts will remove food and healthcare from desperate people," Dodds said in a letter to Starmer posted on X.

On Tuesday, Starmer pledged to raise UK defence spending to 2.5 percent of GDP by 2027 but ordered the overseas development budget to be cut from 0.5 percent to 0.3 percent of gross national income to pay for it.

Dodds said while she believed defence spending needed to be increased as "the post-war global order has come crashing down", she had hoped for a collective discussion on finding the funding.

"Instead, the tactical decision was taken for ODA to absorb the entire burden," she said, referring to overseas development assistance.

Starmer admitted in a reply to her letter that cutting aid funding was "a difficult and painful decision".

"However, protecting our national security must always be the first duty of any government," he added.

Starmer later announced that long-time ally Jenny Chapman would now fill the role of international development minister.

- Deep cuts -

Dodds voiced fears that plans to help the people of Gaza, Ukraine and Sudan, as well as support climate change and vaccination programmes, would now fall by the wayside.

"It will be impossible to maintain these priorities given the depth of the cuts," Dodds warned.

And she said it would "likely lead to a UK pull-out from numerous African, Caribbean and Western Balkan nations".

Starmer sought to allay her concerns, saying his government would "continue to protect vital programmes, including in the world's worst conflict zones".

Dodds is the fourth minister to leave Starmer's cabinet since his Labour party swept to victory in last year's elections, ending 14 years of Conservative rule.

Earlier this month, the UK leader sacked junior health minister Andrew Gwynne for making anti-Semitic, racist and sexist remarks in a WhatsApp chat.

In January, anti-corruption minister Tulip Siddiq resigned after being named in probes in Bangladesh into graft accusations.

And in November, Louise Haigh stepped down as transport secretary after revelations that she pleaded guilty to a criminal offence before becoming a member of parliament.