Sydney  - Australian Defence Minister Joel Fitzgibbon was fighting to keep his job Thursday after admitting he failed to declare trips to China paid for by family friend and prominent local businesswoman Helen Liu.

"This was a mistake, and for that, I apologize," the embattled minister said after being carpeted in Canberra by Education Minister Julia Gillard, who is standing in for Prime Minister Kevin Rudd while he tours abroad.

The embarrassing apology came after military top brass launched an investigation into allegations that junior officers spied on Fitzgibbon and leaked details of his ties to the China-born Liu.

According to the leak, Fitzgibbon rents his Canberra flat from Liu. The leak also claimed Fitzgibbon was a security risk because of his ties to China.

The Liberal Party's Malcolm Turnbull, leader of the opposition, is pushing for the sacking of the defence minister.

"We need to have a defence minister in whom the Australian Defence Force has confidence, in whom the Australian public has confidence and who can work effectively with his department," Turnbull said. "Joel Fitzgibbon can do none of those things." (dpa)