TOYAKO, Japan (AFP) - The United States and Japan called Sunday for urgent action on red-hot oil and food prices that could derail the global economy on the eve of a summit of the world's richest nations.

As US President George W. Bush arrived at this mountain resort, authorities sealed off Japan's northern island of Hokkaido, with demonstrations relegated to its largest city, Sapporo.

Group of Eight leaders will hold three days of talks in the resort town of Toyako that will be dominated by the fragile world economy, global warming and problems ranging from Zimbabwe to North Korea and Iran's nuclear ambitions.

In pre-summit talks, Japanese Prime Minister Yasuo Fukuda said he and Bush had agreed that urgent efforts are needed to tackle surging oil and food prices.

The dual crises "are having a negative impact on the world economy," Fukuda told a joint press conference. "We agreed there's a need for swift efforts on these fronts."

The leaders of the world's two largest economies also touched on climate change, North Korea's nuclear programme and aid to Africa.

Security was formidable across picturesque Hokkaido, with around 21,000 police deployed to protect the leaders as they huddle in a luxury hilltop hotel.

The leaders of the G8 -- Britain, Canada, France, Germany, Japan, Italy, Russia and the United States -- will be joined by those of some 15 other countries including China, India, Brazil, Australia and eight African states for expanded sessions on global warming and poverty alleviation.

German Chancellor Angela Merkel said the G8 leaders would agree on steps to fight the soaring price of food and to guarantee supplies.

The steps will provide short-term relief to the crisis and a long-term strategy to increase world agricultural production.

Rising food prices have pushed 100 million people below the poverty line, the World Bank estimates, and have sparked street riots around the world.

Japanese press reports have said the G8 will agree to set up a task force on the food crisis or create a system of food reserves much like oil stockpiles.

But aid groups warned that record food and oil prices should not be allowed to derail the leaders' talks on Africa on Monday as the crisis had simply worsened the plight of the poor.

On Wednesday, climate change will top the agenda when an expanded group of nations meets.

The leaders are expected to pledge to spearhead efforts to halve emissions of greenhouse gases by 2050 after agreeing a year ago to "consider seriously" that goal.

The Yomiuri Shimbun newspaper said negotiations were in the final stages for a leaders' declaration, saying "the G8 will take the lead in making efforts to halve" emissions or something similar.

Bush, who has argued that the summit is not the right forum to make hard decisions on climate change, said Sunday he would play a "constructive" role in efforts to curb carbon emissions.

But he warned that India and China must be part of any long-term agreement, a long-standing sticking point that renewed pessimism that there would be any breakthrough.

G8 leaders are also expected to "strongly condemn" Zimbabwe President Robert Mugabe in their final statement following his re-election in a June 27 poll that has been widely denounced as a sham, the White House said.

Merkel said in a video statement that the leaders would discuss "how to tighten the sanctions against Zimbabwe" and called for support from African nations.

While Hokkaido will mark Bush's G8 swansong before he leaves office, it will be the first for Fukuda, Russian President Dmitry Medvedev, British Prime Minister Gordon Brown and South Korean President Lee Myung-Bak.

Medvedev is to meet Bush for the first time since his inauguration in May.

Major leaders from the developing world, including Chinese President Hu Jintao, Indian Prime Minister Manmohan Singh and South African President Thabo Mbeki, will also attend G8 events.

But the atmosphere behind closed doors may get heated.

Former Japanese premier Shinzo Abe revealed in an interview that Bush and French President Nicolas Sarkozy had "fierce" arguments at last year's G8 meeting in Germany.

LIKE IT?  LET OTHERS KNOW