Pakistan's envoy has received a letter written by Mohammed Ajmal Amir Iman Kasab, the lone Mumbai attacker in the custody of Mumbai police, in which he claims he is a Pakistani, private Dawn News TV channel quoted foreign ministry sources as saying.

But Pakistan foreign ministry said the letter itself is not ample proof that Kasab is a Pakistani.

India has accused Pakistan-based militant groups of involvement in last month's Mumbai terror attacks, which killed more than 170 people.

While Kasab was captured, the other nine fellow gunmen were killed by Indian commandos.

India claimed all the ten militants are from Pakistan and pressured Pakistan to take actions.

"The Indian government needs to provide ample proof to establish Kasab's identity," Dawn News television quoted.

Indian External Affairs Minister Pranab Mukherjee said yesterday in New Dehli that India has kept all options open and urged Pakistan to do whatever it has committed.

Pakistan Air Force (PAF) said in a statement yesterday that it has enhanced its vigilance "in view of current environment".

US Joint Chiefs of Staff Chairman Admiral Mike Mullen arrived in Islamabad on Monday for a two-day visit.