David Cameron is in Liberia for talks on international development targets and will have a "historic opportunity" to lift 350 million children out of extreme poverty, charities said.

On the third leg of his tour of Africa, the Prime Minister will co-chair a United Nations meeting on what happens after the Millennium Development Goals (MDGs) expire in 2015.

However, backing ambitious targets could fuel anger among Tory backbenchers at plans to raise aid spending to 0.7% of UK GDP.

On Thursday the premier was forced to concede that the defence budget could face more cuts in 2015-16, while the international development budget is protected.

Mr Cameron becomes the first British prime minister to visit Liberia, where he will jointly chair the High Level Panel with the country's president Ellen Johnson-Sirleaf.

He must grasp the opportunity to take major steps towards ending child poverty, leading charities urged. Oxfam's chief executive Barbara Stocking said: "Unpaid taxes by greedy corporations is enough to help poor countries end global hunger three times over. At this meeting, David Cameron should be pushing for an end to global hunger by 2025, and an end to tax dodging which could pay for this and much more. These companies are effectively taking food from hungry mouths."

Melanie Ward, ActionAid's head of advocacy, said: "To his credit, David Cameron has already personally pledged to put women's empowerment at the heart of the successor to the MDGs. Now is the time for him to deliver on that promise. If Cameron achieves one thing in Monrovia, it should be to find ways to lift the barriers stopping women participating in economic development. As long as 50% of the world's population remain unable to play a part in poverty reduction because they are denied the ability to make their own economic decisions and live their lives free from sexual violence, global development will be sluggish and shallow."

Save the Children highlighted growing inequality and weak accountability as two key obstacles to achieving rapid progress. Policy director Brendan Cox said: "If it does its job right this panel will go down in history for setting out a blueprint that finally banishes two of the greatest injustices from our planet - extreme poverty and preventable child deaths.

"This isn't wishful thinking. Building on the amazing process of recent years it is feasible to imagine that in the next two decades no child will die from preventable causes, no child will go to bed hungry and every child will go to school. By committing to these ambitious but achievable targets, the panel can drive progress towards these goals."

Mohamed Bah, country director for Plan International in Liberia, said: "If we want to end poverty, we need to prioritise the 66 million girls out of education. As they stand, the Millennium Development Goals fail adolescent girls - disregarding serious abuses like sexual violence and forced marriage which stop them from going to school."