By Roland Buerk
BBC News, Tokyo
Japan hosts many US troops but is pulling out of the Afghanistan naval mission
Japan's government has pledged $5bn (£3bn) in new aid to Afghanistan over the next five years.
The decision comes days before US President Barack Obama visits Tokyo.
Japan's centre-left government has said it will end a naval refuelling mission in support of US-led efforts in Afghanistan.
Since coming to power in September the government also said it was working on a plan to offer more civilian aid instead.
Japan's government has been working on a plan to offer more aid to Afghanistan since announcing it would end a mission by the Maritime Self Defence Force to supply fuel to assist US-led operations in the country.
Now there is a figure - $5bn (£3bn) over the next five years.
It is likely to be used for job training, helping former Taliban fighters to reintegrate with society, and for agriculture and infrastructure development.
Prime Minister Yukio Hatoyama is expected to discuss details of the scheme with President Obama when he visits Japan on Friday.
Mr Hatoyama took power in September after winning a landslide in a general election which ended more than half a century of almost unbroken power for the conservative Liberal Democratic Party.
His Democratic Party of Japan wants a more equal relationship with the United States.
The alliance, half a century old next year, is critical to Japan's security and a cornerstone of American policy in Asia. One source of tension is the planned relocation of an American military base on the southern island of Okinawa.
The US is resisting Japan's attempts to reopen negotiations, saying it would undermine a broader agreement to a reorganise the nearly 50,000 strong American force in the country.