Rakesh Maria, a top Mumbai police official, had previously said that Indian police was "quite hopeful" of bringing formal charges against Kasab before January 24 - 60 days after his initial detention.
Police have up to 90 days from the date of the suspect's arrest to file charges.
The deadly attacks on several Mumbai landmarks, including two famous hotels and a busy railway station, strained relations between India and Pakistan and triggered a war of words between the two nuclear rivals.
Indian officials insist that the attacks could not have taken place without the knowledge of senior figures in Pakistan.
However, Islamabad has denied any involvement.