India has tightened its borders tremendously, National Security Adviser M K Narayanan told a media conference on board Air India 001 carrying Prime Minister Manmohan Singh to his summit with Russian President Vladimir Putin in Moscow.

"We are on guard," Narayanan said, responding to the current upheaval in Pakistan, adding that cross-border infiltration has increased in recent weeks.

"We were very proud that infiltration had decreased," the national security adviser said, "but two, three bad incidents have indicated that infiltration is on the increase."

"We are very worried about what is happening in Pakistan," Narayanan said, adding that infiltration and the uncertain situation across the border "crimps our drive to cut troops" in Jammu and Kashmir.