Last night (15/08/2013) I was out on my balcony smoking a cigarette, facing the direction of the Frankfurt International Airport, when 3 aircraft caught my attention. I could plainly identify a commercial airplane flying in a normal fashion... But what caught my attention was 2 other aircraft i couldnt identify approaching this airplane at a high rate of speed. One was ascending at a 45 degree angle to the jet, and the other was a bit lower than the jet. They slowed down to the speed of the airplane, circled it, FLASHED a light at the airplane, and took off at an incredible speed. I ran inside to tell my girlfriend who was just stepping out of the shower at the time, but by the time we both came back outside they were gone. The whole event only lasted a couple minutes. This is not the first time I witnessed strange objects flying over our airport. And they always seem to come in groups of 5 or more...