India says the sole surviving gunman from last month's attacks Mumbai (Bombay) has sought help from Pakistan. The request came in a letter given to Pakistani diplomats in Delhi.
Indian officials said Mohammed Ajmal Amir Qasab, who is in custody, admitted in the letter that he and the other attackers were from Pakistan.
Pakistani officials say they are studying the contents of the letter.
Islamabad has so far refused to acknowledge the gunmen were Pakistani.
Relations between the two countries have been severely strained since the attacks, in which more than 170 people were killed.
India blames the Pakistan-based group Lashkar-e-Taiba (LeT) for the attacks, which began on 26 November and lasted three days.
Last week, President Asif Ali Zardari of Pakistan said reports that the sole surviving attacker had been identified by his own father as coming from Pakistan had not been proven.
Two hotels in the attacks, the Trident-Oberoi and Taj Mahal Palace, reopened for business on Sunday.