Henry Rotich is accused of flouting procurement procedures in awarding a contract worth over $450m (£405m) for the construction of two dams to the Italian company CMC de Ravenna.

In March Mr Rotich denied any wrongdoing in a large newspaper advert.

The company has also denied the accusations.

Director of public prosecutions Noordin Haji is also investigating how the tender was awarded for $170m more than was in the original contract.

"It was established that the conception, procurement and payment process for the dam projects were riddled with massive illegalities," he said.

He has ordered the arrest of more than 20 other people accused of being involved in the contract, including other top officials and the directors of CMC de Ravenna.