The United States put up $10 billion to rebuild Afghanistan on Thursday as world donors responded to a funding appeal from President Hamid Karzai but warned more must be done to fight corruption.

Karzai sought support to finance part of a $50 billion development plan over the next five years to counter widespread poverty and a Taliban insurgency.

"What brings us together today is a concern for the destiny of a nation that has emerged from a dark past," Karzai told donors from more than 80 countries and international institutions in Paris.

Announcing a $10.2 billion contribution, US First Lady Laura Bush said that "Afghanistan has reached a decisive moment for its future. We must not turn our backs on this opportunity."

President Nicolas Sarkozy announced French financial aid would be "more than doubled" with priority given to agriculture and health, bringing assistance up to 107 million euros ($165 million) over the next two years.

Japan doubled its aid to reach $550 million while Germany put up 420 million euros over the next two years. The World Bank said it would channel about $1.1 billion over five years.

US officials said they expected $15 billion (9.7 billion euros) to be raised, but European and UN diplomats stressed the conference must also tackle the more sensitive issue of how the funds are spent.

"While Afghanistan needs large amounts of aid, precisely how aid is spent is just as important," said Karzai.

Facing a presidential election next year, the Afghan leader is under pressure over his apparent inability to deal with corruption and opium production, seen as prolonging the Taliban insurgency.

UN Secretary General Ban Ki-moon called for "active measures" to be taken to fight corruption, guarantee transparency and ensure that financial aid reaches those who need it.

"It is only by combating corruption and strengthening the rule of law that our commitment will be efficient," stressed German Foreign Minister Frank Walter Steinmeier.

More than six years after US-led forces ousted the Taliban, Afghanistan remains mired in poverty and its people lack many basics while the extremist militia has pushed on with its insurgency in the south.

Some 47,000 troops from a NATO-led force are fighting the Taliban alongside 20,000 US troops. The violence has left 8,000 people dead in 2007 alone including 1,500 civilians, according to UN figures.

Listing progress in building roads and clinics, fighting opium production and setting up a functioning government, Karzai nevertheless acknowledged: "There is a long way still ahead of us."

With a development plan on the table, Afghanistan needs "adequate, long term and predictable support," said Karzai.

Security remains Afghanistan's biggest challenge, he said, arguing that his government was fighting "international terrorists" funded from abroad, a reference to neighbouring Pakistan.

Karzai's ambitious blueprint focuses first on infrastructure, with plans to build roads, dams and power plants, but building up the army and security forces is also a priority along with developing agriculture.

Relief organisations have complained that too much international aid is spent on security while development projects vital to fight poverty and strengthen the state are neglected.

A report by an umbrella group of aid organisations warned in March that only $15 billion out of the $25 billion promised in donations since the 2001 fall of the Taliban had been released.

Forty percent of that amount returned to donor nations to cover consultant fees and projects carried out by various private contractors, according to the report by ACBAR, the Agency Coordinating Body for Afghan Relief.