A federal judge has reportedly frozen some accounts controlled by Enron's former chief financial officer, Andrew Fastow, and some of his family.

US magistrate judge Calvin Botley signed the order late on Thursday in Houston to prevent Mr Fastow or other family members from moving money, according to a report in the Houston Chronicle.

In court documents unveiled on Wednesday, federal prosecutors said they would try to seize at least $23m from Mr Fastow and others.

Mr Fastow's role in Enron's collapse is now coming under intense scrutiny. It is not unusual in a case where the financial stakes are high for the prosecutors to secure money they believe might be hidden.

Guilty plea

Earlier this week, Michael Kopper - Fastow's right hand man - pleaded guilty to charges of money laundering and wire fraud.

The guilty pleas are the first criminal charges brought against a former Enron employee, and represent significant progress in the US Government investigation into the scandal.

Enron was once one of the US's most admired companies, but went bankrupt last December after admitting to questionable accounting practices.

Mr Kopper worked in Enron's Global Finance unit and took a lead role in the formation of the off-balance-sheet partnerships central to Enron's collapse.

These partnerships were used to hide $1bn of debt, and make the company look financially stronger than it actually was.

An internal investigation by Enron directors blamed Mr Fastow for creating and operating the partnerships.