Police are investigating the alleged rape of a prostitute and a separate assault both involving visiting US servicemen on a wild night out in Sydney.
A US sailor has been accused of raping a prostitute over the weekend while another is in a coma after an apparent road rage attack.
Detectives are working on both cases and are believed to have alerted the US Navy to the rape allegations.
"Police are investigating a claim of assault at a Kings Cross brothel at the weekend," a police spokesman said.
The woman was allegedly attacked last night but it is believed police are yet to formally speak with the victim.
The US Embassy has confirmed a serviceman from the USS Peleliu is being investigated over the alleged assault on the prostitute but no charges have been laid.
Meanwhile a 23-year-old Marine was attacked around 2am Sunday after blocking the path of a car at Kings Cross.
The Marine was ushered off the road by a passer-by before a passenger in the car allegedly got out and punched him in the face, causing him to fall heavily and hit his head.
The victim suffered a fractured skull and other injuries and is in a serious but stable condition in St Vincents Hospital.
More than 3000 Marines have come ashore in Sydney this month with the arrival of the amphibious assault ship USS Peleliu and the guided missile destroyer USS Halsey.