The majority of the published attacks on reduced-round variants of block ciphers seeks to maximize the number of rounds to be broken, using less data than the entire codebook and less time than exhaustive key search. In this paper, a novel key partitioningchosen plaintext attack against reduced-rounds AES variants up to 3 rounds that uses only 33 chosen plaintext-ciphertext pairs, a workload of 219(for three round variant) and 217bytes of memory is introduced. The attack depends upon the internal structure of the AES round function, the differential characteristics of the AES S-BOX and thekey partitioning in which each key byte will be processed individually independent to the other key bytes. To clarify the idea of the attack we will follow a round by round cryptanalysis till the third round of the AES. The results gives that a bit-level permutation is more efficient than byte-level permutation used in the AES round function.We also introduce a counter measure for this attack by using a bit-level permutation on the AES round function instead a byte level permutation.