TOKYO - Major donors pledged on Sunday to give Afghanistan $16 billion in development aid over the next four years as they seek to prevent it from sliding back into chaos when foreign troops leave, but demanded reforms to fight widespread corruption.

Donor fatigue and war weariness have taken their toll on how long the global community is willing to support Afghanistan and there are concerns about security following the withdrawal of most NATO troops in 2014 if financial backing is not secured.

"Afghanistan's security cannot only be measured by the absence of war," US Secretary of State Hillary Clinton told an international donors' conference in Tokyo.

"It has to be measured by whether people have jobs and economic opportunity, whether they believe their government is serving their needs, whether political reconciliation proceeds and succeeds."

The Afghan central bank has estimated that at least $6 billion a year in new investment from foreign donors will be needed to foster economic growth over the next decade.

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