Yousaf Raza Gilani also said Pakistan needed more help from other nations to increase its effectiveness in battling militants along its border with Afghanistan, according to an interview carried in the FT's weekend edition.
India and Pakistan have been exchanging heated rhetoric and threats since the Mumbai attacks that killed 179 people in November, which India says were not only carried out by Pakistani nationals but must have had support from Pakistani state agencies.
Pakistan "needed to act fast" to ease tensions, and "if somebody is out of the country and he has proved to be guilty, then certainly we have to look into our own laws as well," Gilani was quoted as saying.
Pakistan has said it would not send any attackers who might be arrested to India for prosecution, which New Delhi would prefer.
Gilani repeated past pledges to co-operate fully with India in the investigation of the Mumbai attack, and to share and publicise its findings.
Pakistan has also been under pressure from allies like the United States to crack down on militants along its border with Afghanistan. Gilani told the FT it had only limited resources to do so and aid would help.
"You are fighting war in Afghanistan with the most sophisticated weapons in the world and the whole world is pouring money into that," Gilani was quoted as saying.
"When it comes to Pakistan, the world should understand that they have to build up the capacity of Pakistan too."
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