Christian Aid is calling on the new Prime Minister to restore the international aid budget.
In a statement, the charity's Chief Executive said Mr Sunak mustn't balance the books on the back of the poorest people and should instead reset the government's aid commitments.
In 2020 while he was Chancellor, Rishi Sunak cut the international aid budget from 0.7 percent to 0.5 per cent despite the higher level being enshrined in law. That broke a manifesto pledge and represented a decrease of $4.5 billion. Mr Sunak said he made the decision because the UK was in an unprecedented time of crisis because of the pandemic. He said he hoped the 0.7 per cent target could be restored when the UK's finances allowed it.
The reduction meant that aid to Syria for example was cut by 69 per cent.
Speaking after Rishi Sunak was appointed Britain's Prime Minister, Patrick Watt said:"In the face of the worst global cost of living crisis in a generation, the new Prime Minister must re-set the government's approach. We need a commitment that he will not balance the books on the back of the poorest people, either at home or abroad.
"With COP27 on the horizon, Rishi Sunak must show leadership on the climate crisis by supporting a swift just transition to net zero while also urgently helping the millions of people on the brink of famine in East Africa by restoring the aid budget."
Rains have failed for the fourth consecutive year in East Africa threatening millions with starvation.