India says the sole surviving gunman from last month's Mumbai (Bombay) attacks has sought help from Pakistan, BBC reported.
The request came in a letter handed to Pakistani diplomats in Delhi.
Mohammed Ajmal Amir Qasab, who is in Indian custody, admitted in the letter that he and the other attackers were from Pakistan, Indian officials said.
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.
Earlier, India's Foreign Minister Pranab Mukherjee said the international community had not done enough to exert pressure on Pakistan, which denies any involvement in the attacks.
On Monday fighter jets flew low over three major cities in Pakistan amid the heightened tension.
India's foreign ministry said the acting high commissioner of Pakistan had been handed the letter from the gunman on Monday evening.
"In his letter addressed to the Pakistan High Commission, Kasab [Qasab] has stated that he and the other terrorists killed in the attack were from Pakistan and has sought a meeting with the Pakistan High Commission," the ministry said.
Reports suggested the letter contained a request for legal help from Pakistan. Indian lawyers have so far refused to represent Mr Qasab in court.
Pakistani officials confirmed receipt of the letter and said they were examining its contents.
The Pakistani government is under intense pressure to act decisively against militants operating on its soil.
Addressing Indian envoys from across the world, Mr Mukherjee accused Islamabad of "denial" and "shifting the blame" for last month's attacks.
"We have so far acted with utmost restraint and are hopeful that international community will use its influence to urge the Pakistani government to take effective action."
But Mr Mukherjee said that although there had been "some effort so far by the international community... this is not enough. Much more needs to be done."
His statement was the latest in a series of strongly worded diplomatic warnings from India.
The BBC's Chris Morris in Delhi says the Indian government is clearly determined to maintain pressure on Islamabad to act.
India has blamed Pakistan-based militant group Lashkar-e-Taiba (LeT) for the attacks, which began on 26 November and lasted three days.
Last week, Pakistan's President Asif Ali Zardari said claims that the sole surviving attacker had been identified by his own father as coming from Pakistan had not been proven.
The two hotels caught up in the attacks, the Trident-Oberoi and Taj Mahal Palace, reopened for business on Sunday.