US retail group Saks Inc says it is carrying out a more intensive investigation than initially planned into vendor payments at its Saks Fifth Avenue division.

The company said that its audit committee would look over when markdown allowances were logged, and whether or not suppliers were falsely charged for not following Saks's rules on logistics, billing or transportation.

Saks will also look at whether any over-collections of markdown allowances were made in merchandise segments not included in the committee's previous probe.

Suppliers give stores markdown money to compensate for goods that don't sell, causing bigger than expected reductions.

Saks reported in May that it had laid off its chief accounting officer along with other key officers after an internal probe found that $20 million was illegitimately taken from Vendors between 1999 and 2004.

The Saks group is also being probed by the Securities and Exchange Commission and US Attorney's Office in New York.