Four secret service agents were injured in New Hampshire on Tuesday after a driver crossed double-yellow lines and crashed head-on with the agents' vehicle.

CNN reports the unnamed agents were transported to Frisbee Memorial Hospital for treatment.

"At this time, our personnel have sustained what is described as serious, but non life threatening injuries," Secret Service Director Joseph Clancy said in a statement. "Please join us as we keep all the victims of this accident and their families in our thoughts and prayers."

The agents were on active duty, traveling in a Ford Taurus on Route 16, when the driver of a Mercury Sable attempted to cross into their lane, causing the collision with their vehicle.

The Washington Post reports the driver, who later died at the scene, was identified as 45-year-old Bruce Danforth. He reportedly lacked a valid driver's license and had an "extensive criminal history," according to the Wakefield Police Department.

Two other passengers in Danforth's vehicle -- Natasha Meroski, 35, and Kristina Buswell, 21 -- were taken to the hospital for injuries.

Presidential candidate Hillary Clinton appeared in New Hampshire around the time of the crash. Some speculated that the agents may have been part of the Democratic candidate's security detail. 

However, the four men were actually part of a "jump team," providing additional security and standing post at campaign events. The agents are believed to have worked out of field offices somewhere in the New England area.

Clinton later released a statement on the incident.

"I was saddened and concerned to hear about the serious accident that occurred last night. My husband and I send our prayers and condolences to all the victims and their families. We are grateful everyday for the service, dedication, and professionalism of the U.S. Secret Service," Clinton said.