Two parachutists free-falling at 120 mph in the United Kingdom had a near miss with two U.S. fighter jets that zoomed below them, a report of the incident says.

The F-15 fighter jet pilots were unaware they were flying near an active parachute site over Chatteris in Cambridgeshire, and air traffic controls did not warn them ahead of the April incident, according to the recent report from the UK Airprox Board.

The board, part of the U.K.'s Civil Aviation Authority, said that regulations, processes, procedures and compliance were deemed ineffective at various points during the incident, and it was classified in the second-highest danger category.

According to the report, the F-15 pilots changed course slightly to avoid a refueling aircraft. The turn occurred during a hand over from RAF Coningsby to an air traffic controller at RAF Lakenheath, home to the 48th Fighter Wing.

The air traffic controller thought he would have "plenty of time" to change the jets' course, but "the frequency became busy just as they transferred and so, by the time the

F15 pilots checked in with the controller, they were already about to fly over Chatteris," the report says.

How can veterans cope with PTSD?:Some are turning to beekeeping

Florida 'fortune teller':Ordered to repay $1.6 million to woman she convinced was cursed

The UK Airprox Board said the pilots should have been aware that there could have been an active parachute drop and should have either asked the controller ahead of time or avoided the area.

The board also saw Go-Pro footage from one of the parachutists' helmets in which the board "could clearly see the F15s passing beneath," but it was hard to determine how close the jets were, the report says.

"Once the parachutists had seen the F15s there was very little they could do to avoid the situation, having no control over their speed or direction whilst in free-fall," the report says. The board said officials at Chatteris and the para-dropping aircraft could not have done more to avoid the situation.

The report says crews were being re-briefed on the parachute site.

Col. Will Marshall, 48th Fighter Wing commander, said in a statement that "U.K. airspace is incredibly complex and often congested."

"The safety of our aircrew as well as those we share the skies with is our number one priority," he added. "We are using this incident to reinforce the vital importance of situational awareness and attention to detail for our all of our air traffic controllers and aircrew."

Follow USA TODAY's Ryan Miller on Twitter @RyanW_Miller