Kenya president Mwai Kibaki has promised to stop corruption

Kenyan Energy Minister Ochillo Ayacko said the government would look into procurements made by the four firms, and claimed workers had "abused" business practices under the previous government.

President Mwai Kibaki and his National Rainbow Coalition swept to power in last year's elections on an anti-corruption platform.

We are pressing for affordable tariffs Kenyan Energy Minister Ochillo Ayacko

Mr Kibaki promised to stamp out corruption and rebuild the country's economy following the 39-year rule of president Daniel arap Moi's Kenya African National Union.

Kenyan power costs are said to be among the highest in Africa.

Mr Ayacko said he wanted to halve the tariffs charged by the country's two main independent power producers in an effort to reduce consumers' electricity bills.

'Gross abuse'

The companies under investigation include the country's main electricity utility Kenya Power and Lighting (KPLC), Kenya Electricity Generating, Kenya Pipeline and National Oil Corp.

Mr Ayacko said the companies' managers would be investigated, saying they had taken advantage of "gross abuse of business practices by politically correct individuals during the KANU (Kenya African National Union) regime to plunder their assets".

For the last seven years of Mr Moi's rule, the four companies were exempt from parliamentary scrutiny.

It was during this time that KPLC lost money and invested $10m of its employees' pension money in the Spanish independent power producer, Iberafrica.

In February, Mr Ayacko replaced KPLC's top management.

The Kenyan government has a 51% stake in KPLC.