The UK will use £200 million of aid money to help African countries tackle the migrant crisis.
British government sources said David Cameron would set out his plan over the working dinner at an international summit aimed at addressing the problem.
The Prime Minister will urge an "emergency response" to the crisis as he sets out the extra money up to 2020. The funding will be used to help African countries cope with economic pressures, environmental disasters such as droughts and problems of corruption.
The money, announced during the Valletta summit on migration, will also be used to provide humanitarian support for refugees.
The Government will provide £125 million to Ethiopia, which has seen its refugee population soar from 90,000 in 2011 to 700,000 in 2015.
Some £5 million will be used to provide life-saving humanitarian assistance in the Sahel countries such as Mali and Burkina Faso, with the money providing food, water and shelter.
As part of the drive to tackle the root causes of the problem, a £13 million programme will create 9,000 jobs in Somalia, giving them the option of choosing to "stay where they are and not be coming to Europe".
But as well as the extra funding for African nations, the Government will also urge them to do more to accept the return of migrants who have tried to enter the European Union illegally.
"The Prime Minister will be emphasising to the Africans that they have got to work with us on returns. We welcome the co-operation they have shown so far but it's very important that we develop the situation where we are able to return illegal migrants who arrive in the Mediterranean," the source said.
The UK will also provide three million euros (£2.1 million) to a trust fund for Africa being set up by the European Commission.
The extra support for Africa came after Mr Cameron vowed the UK will play a "huge and historic role" in helping to tackle the migration crisis, including stepping up efforts to "smash" gangs of human traffickers.
The Prime Minister said it was "the biggest problem facing Europe today", with a movement of people greater than any seen since the end of the Second World War.
He called for a new "resolve" to tackle the problem as he addressed the company of Royal Navy warship HMS Bulwark in Valletta harbour.
He said: "We need to smash those gangs and that is what the next stage of this work is going to be about. It will be difficult work but it's absolutely essential and we will give you everything you need to make sure that work gets done properly.
"In the end we have to break the link between getting on the boat and getting the chance to come to Europe. As long as that ability to do that is there, the criminal gangs keep on exploiting people in the way they are today.
"So we know what needs to be done - the humanity of a moral nation, the partnership of a country that acts with others to get things done in the world and a country that knows resolve is going to be absolutely key to dealing with this."
Amphibious assault ship HMS Bulwark was despatched to the Mediterranean in April to help rescue migrants attempting the treacherous crossing from North Africa to Europe.
Mr Cameron told the crew: "You should be incredibly proud of the lives you have saved. There will be people who will live out extraordinary dreams and lives that wouldn't have happened were it not for what you have done in the Mediterranean."