The World Bank has launched a disciplinary investigation against one of its high-ranking economists after he criticised the bank's record on tackling poverty.

William Easterly attacked the bank's record in a recent book and an article in the Financial Times. He is just one of a number of critics who have attacked the bank.

Easterly said in the FT that the $1 trillion (£685 billion) spent on aid since the 1960s with the assistance of the World Bank and others had failed to attain the desired results.

In his book, The Elusive Quest for Growth, Easterly is critical of the bank's history of fighting poverty.

"Sub-Saharan Africa has not emerged from a decades-long economic crises; Asia remains the home of the majority of the world's poor; Latin America has known only erratic and low growth; the Middle East has not convered oil riches into sustained developement. It is little wonder that protesters have demonstrated so vehemently against the international organisations," he wrote.

Easterly is a senior advisor to the bank's research group and has helped to determine its anti-poverty strategy for the past 16 years.

The bank describes its investigation as a routine enforcement of its media and communications policy. The investigation comes as the bank's president, James Wolfensohn, faces increasing pressure from critics.