David Cameron has a "historic opportunity" to lift 350 million children out of extreme poverty, charities said, as he attends an international development conference in Liberia.

The Prime Minister is co-chairing the United Nations' High Level Panel meeting, which is considering what new targets to set once Millennium Development Goals (MDGs) expire in 2015.

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."

Melanie Ward, head of advocacy at ActionAid, 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."

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.

"In Liberia this week, Plan heard global children and youth campaigners identify girls' education and ending early and forced marriage as priorities. They also stressed the need for sexual and reproductive health services and for those with disabilities to be included.

"From Plan's experience, a girl who has completed nine years of schooling is less likely to marry young and have children before she is ready. She is more likely to know her rights, be healthy and reinvest her income into her family, community and country. We must build on the current success of the Millennium Development Goals and take them further."