An ally of Senate candidate Roy Moore detailed a visit to a Vietnamese brothel with "very young" girls as a way of illustrating the Republican’s ethical rectitude.

Alabamans are casting ballots for their next US Senator, concluding a race that has been roiled by allegations that Mr Moore engaged in sexual misconduct with teenage girls. The Republican has strenuously denied those allegations, saying “I have never engaged in sexual misconduct” and casting the accusations as a partisan assault on his candidacy.

In an effort to demonstrate the candidate’s moral fire, Bill Staehle relayed a story from when he and Mr Moore were serving in Vietnam. They accompanied a fellow service member who would soon be departing the country on a night out and quickly realised what the evening would entail.

“He took us to this place which turned out to be a brothel,” Mr Staehle told a rally.

“There were certainly pretty girls, and they were girls and they were young, some of them probably very young,” he added.

But even before the young women could approach, Mr Staehle said, Mr Moore “said to me we shouldn’t be here, I’m leaving”.