RAF MILDENHALL, England — An Air Force special operations airman remained hospitalized Tuesday with head injuries two days after he was allegedly attacked by a group of British men just off base, authorities said.

He and another airman from the 352nd Special Operations Group were injured early Sunday morning in what authorities have preliminarily described as an unprovoked attack in the town of Mildenhall, according to the Suffolk Constabulary.

The second airman was treated and released from Cambridge’s Addenbrooke’s Hospital, authorities said.

The injured airmen’s names were not released on Tuesday.

Master Sgt. Dennis Brewer, a spokesman for the 352nd SOG, said he wasn’t sure whether the airman who was released from the hospital was back at work.

The incident occurred between midnight and 1 a.m. on a street in Mildenhall, which is roughly a mile from the RAF Mildenhall perimeter.

Police have arrested four British men, according to Suffolk Constabulary spokewoman Lisa Crane. Three suspects were apprehended shortly after the alleged attack while a fourth was detained after the initial police inquiry, she said.

The four men are scheduled to appear at the Bury St. Edmunds police station on Feb. 13. British law enforcement officials will decide whether the men will face formal charges or be released without charges, or if further investigation is required, Crane said.

Crane said the Suffolk Constabulary is still seeking witnesses. Anyone with information is urged to contact the Suffolk Constabulary at 0800 555 111.

Sunday’s alleged assault is the second time British nationals have been investigated for attacking American airmen in Suffolk in the past year.

Two Cambridge men, Edward Harper and William Harper, are slated to appear in British court on Feb. 20, charged with assaulting two RAF Mildenhall airmen outside of a Newmarket nightclub last summer.