Pakistan Air Force fighter jets intruded into Indian air space thrice in 2005, forcing India to take counter measures, Defence Minister Pranab Mukherjee informed the Lok Sabha on Thursday.
One incident occurred in January, while two more violations were reported in March, the minister said in a written reply.
He added that a protest had been lodged through diplomatic channels.
Asked what India's response was, Mukherjee said, "Required air defence measures are initiated depending upon the situation."
He, however, did not specify the sectors where the intrusions had taken place.
Speaking on a different issue, the minister informed the House that a memorandum of agreement had been signed with the United States for training, research and conducting bilateral workshops in the field of medicine.
"This collaboration will help in expanding and upgrading the knowledge of the Indian Armed Forces Medical Services, especially in certain frontier areas of medicine," Mukherjee said.
On the spate of incidents of fire in military ammunition depots during the last three years, the minister said ammunition worth more than Rs 81 crore was lost at three main depots in Jodhpur, Amla and Pulgoan.
He said as part of new safety measures, services were shifting unserviceable ammunition on a priority basis.