The Kenyan government says it has traced $1bn in the foreign accounts of three unnamed Kenyans.
Mr Murungi said it could prove costly to recover the money
Justice Minister Kiraitu Murungi said that naming the individuals concerned at this stage could jeopardise the investigation.
He said the money had been siphoned out of Kenya through corrupt deals under former President Daniel arap Moi.
President Mwai Kibaki has pledged to make the fight against corruption a key part of his programme.
Mr Murungi said that investigators based in Britain had been hired to look into the situation, and could uncover a further $2bn held by Kenyan businessmen in foreign accounts.
But he said it could be costly to recover the money.
Last week, four senior officials were suspended amid an investigation into a contraversial tender for passport-making equipment.
Corruption watchdog Transparency International says that police corruption has fallen since Mr Kibaki took over in December 2002.