A deputy U.S. Marshal traveling to London to help extradite a criminal defendant has been taken into custody by British authorities after he was accused of sexually abusing a female passenger on board a Delta flight, four law enforcement officials said.

The federal marshal was one of two deputies traveling on a Delta flight from New York City’s JFK Airport to London when the woman complained to the flight crew that she had been inappropriately touched during the flight, the sources said.

A Delta Airlines spokesman confirmed there was an incident on board the flight.

“Due to unruly passenger behavior while in flight, Delta Flight 1, JFK to London-Heathrow was met by local law enforcement upon landing and Delta is cooperating with their investigation,” the spokesperson said.

Two law enforcement sources said the two federal marshals had been drinking during the flight. The second marshal was being sent back to New York Wednesday night without facing any charges.

Both deputies are assigned to the Eastern District of New York and were en route to London to bring back a suspect wanted in Brooklyn on federal fraud-related charges.

A statement from the Metropolitan Police in London said their officers at Heathrow Airport were informed that the marshal had “sexually assaulted other passengers and crew” aboard the flight, adding that the 39-year-old was arrested on suspicion of sexual assault and remains in custody.

A spokesman for the US Marshals Service said they were aware that the officer “exhibited inappropriate behavior while intoxicated on an inbound flight.” The spokesperson added that the Marshals Service is cooperating with UK law enforcement and other agencies regarding the alleged incident.

“The U.S. Marshals Service takes seriously any allegations of misconduct by its employees. The alleged actions of the employees do not reflect the professionalism of the thousands of employees of the USMS or its core values,” the statement read.