UN Secretary General Ban Ki-Moon, World Bank President Robert Zoellick and African Union commission chief Jean Ping also attended the talks.
All of them appealed to the G8 leaders not to abandon Africa by backtracking on a previous pledge to raise the amount of aid given to the continent.
"High food prices are already turning back the clock on development gains. To avoid further suffering, we are calling on world leaders to deliver a full range of immediate needs, including food assistance," said Ban.
"The world faces three simultaneous crises -- a food crisis, a climate crisis and a development crisis," Ban told reporters. "The three crises are deeply interconnected and need to be addressed as such."
"Summits cannot solve all the world's ills ... but I believe this summit can make an important start, here and now, to focus on the needs of the most vulnerable," Zoellick added.
Merkel demands action on food and fuel crises
German Chancellor Angela Merkel said the African leaders demanded action as the global food and fuel crisis has hit the continent's most vulnerable people the hardest.
"The African countries expressed their fears that many of the Millennium Development Goals will be more difficult to reach if commodity prices keep rising like they are at the moment," she told reporters.
Japanese officials said African leaders had been unanimous in urging the G8 to stick to their 2005 pledge to raise annual aid to developing countries by 50 billion dollars by 2010.
But Ban noted that as much as 62 billion dollars per year would be needed by then in order to meet the Millennium Development Goals - a series of UN-sponsored targets which include halving the number of starving people by 2015.
The aid group Oxfam quoted sources as saying G8 negotiators were late Monday deadlocked on the issue of aid promises to Africa.
The draft text of a communiqué on development does not include a reiteration of a promise by G8 leaders three years ago to provide 50 billion dollars extra in aid by 2010, half of it earmarked for Africa. "We must see the 50 billion dollars aid promise back in the communiqué," said Max Lawson of Oxfam International.
All sides acknowledged that the problem of hunger, spiraling food and oil prices and the impact of global warming are strictly related.
Energy targets causing strife between members
But while European Union Commission President Jose Manuel Barroso urged G8 leaders to agree on "meaningful," "ambitious" and "binding" long-term targets for cutting greenhouse gas emissions, Germany found itself isolated as the United States, backed by six other G8 members, pointed to the building of more nuclear power plants as a possible way out.
Briefing the press on the sidelines of the G8, US President George W Bush's environment advisor, Jim Connaughton, stressed the "green" properties of nuclear energy.
"There is no question ... that nuclear energy, responsibly developed by countries capable of managing it, is an essential component of cutting greenhouse gas emissions," Connaughton said.
While France, Britain, Canada, Italy, Russia are all broadly in favor of nuclear energy, the German government has only just agreed to phase out its nuclear reactors by 2021.
Despite Angela Merkel, the chancellor, being herself in favor of atomic energy, it is widely unpopular among the German electorate.
"Nuclear power is not the main factor in trying to protect the environment," she told German reporters as she moved to prevent the summit from making a reference to nuclear energy in its final communiqué.
Climate and economy on second day's agenda
Climate change was to feature more prominently on Tuesday, when G8 leaders were due to turn to the main items on their official agenda.
Among them is the slowdown in the global economy and accelerating inflation.
Monday's opening day was preceded by a series of bilateral meetings, most notably between Bush and Russian President Dmitry Medvedev, who was described as "a smart guy" by his American counterpart.
