Avoiding code duplication in F#

I have two snippets of code that tries to convert a float list to a Vector3 or Vector2 list. The idea is to take 2/3 elements at a time from the list and combine them as a vector. The end result is a sequence of vectors.

    let rec vec3Seq floatList =
        seq {
            match floatList with
            | x::y::z::tail -> yield Vector3(x,y,z)
                               yield! vec3Seq tail
            | [] -> ()
            | _ -> failwith "float array not multiple of 3?"
            }

    let rec vec2Seq floatList =
        seq {
            match floatList with
            | x::y::tail -> yield Vector2(x,y)
                            yield! vec2Seq tail
            | [] -> ()
            | _ -> failwith "float array not multiple of 2?"
            }

The code looks very similiar and yet there seems to be no way to extract a common portion. Any ideas?