Former PM Howard backs Sinodinos

Former prime minister John Howard has backed embattled Liberal senator Arthur Sinodinos as a man of great integrity.

The assistant treasurer is facing Labor calls to provide further detail of his role in Australian Water Holdings, which is the subject of a NSW Independent Commission Against Corruption inquiry.

"Arthur Sinodinos is a man of great integrity and ability," Mr Howard said in a statement regarding his former chief-of-staff, adding he continued to hold him in the highest regard.

"As he has indicated that he will answer questions at the ICAC inquiry it is not appropriate that I comment on the substance of the matter."