Foreign Office spokesman Nafees Zakaria made the remarks at a media briefing here, a day after Aseemanand was acquitted along with six others in the 2007 Ajmer blast case.
"Aseemanand and Col Rohit were involved in the Samjhauta Express tragedy... Aseemanand himself confessed to the crime," Zakaria said.
A total of 68 people, mostly Pakistani nationals, were killed in the blasts in two coaches of Samjhauta Express train in Panipat on February 18, 2007. Aseemanand is an accused in the case.
Commenting on the issue of national security, Zakaria said Pakistan would maintain minimum deterrence capability.
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He said the Nuclear Suppliers Group while considering membership of India should know that India was one of the largest buyers of weapons.
"India's massive arms build-up and testing of inter-continental ballistic missiles is the source of concern for the region," he said, adding that Pakistan would not indulge in any arms race.
Zakaria also claimed that India was trying to deflect the world's attention from alleged atrocities in Kashmir by firing on the Line of Control.
He said the upcoming meeting of Permanent Indus Water Commissioners of India and Pakistan was a regular feature under the Indus Waters Treaty.