The soaring price of basic foods such as rice – the benchmark Thai variety now fetches some $1,000 a tonne, up threefold on a year ago - has led to a supply crunch that is worrying governments wary of popular unrest.

There are other tough issues facing the bank, notably a simmering internal row among its members over its continuing relevance in a region that has been transformed since the lender was founded 42 years ago.

The United States, which with Japan is the ADB's largest shareholder, took the unprecedented recent step of voting against its long-term strategic plan, which is also on the agenda for the meeting in Spain's capital Madrid.

But a source within the bank, who asked not to be named, said, "While the bank faces a number of critical issues about its role and relevance, all this may be overshadowed by the food crisis."

ADB president Haruhiko Kuroda warned recently that soaring food prices had pushed back Asia's fight against poverty, and that some countries may one day need foreign aid to feed their hungry.

The rises are blamed on higher energy and fertilizer costs, greater global demand, droughts, the loss of rice farmland to biofuel plantations and price speculation.

"The food crisis did not happen overnight," said Shalmali Guttal, a senior associate at Focus on the Global South, a Bangkok-based political and economic advocacy group.