A US embassy staffer was smuggled out of the UK in August following allegations of possessing indecent images of children, the BBC reported on Sunday.
According to the BBC, the embassy staffer had been detained in his apartment before leaving the country, which occured before British police could interrogate him.
The US Embassy in London told the BBC that the staffer was reassigned to a US-based position while the issue is investigated.
"The United States government expects all personnel to adhere to the highest standards of conduct," embassy officials said. "We take these allegations seriously."
The officials said they "took swift action" after learning of the allegations and "quickly informed UK law enforcement," with the US investigation being conducted in conjunction with the UK.
Staffer flown back to US on commercial flight as investigation continues
The BBC added that the staffer, who was flown back to the US on a commercial flight, has diplomatic protections despite not being a diplomat.
A spokesperson for the UK government was cited as saying that the country expects "all foreign diplomats in the UK to abide by our laws, in the same way we expect all UK diplomats to do so when posted overseas."
Amid the investigation, Home Office ministers and the Metropolitan Police are remaining in contact with the US Embassy in London, the BBC added.