India did essentially need civil-nuclear cooperation with the US for its energy requirements, but the deal it sealed during President George Bush's [Images] visit has instead capped New Delhi's deterrence capabilities, former national security advisor Brajesh Mishra has said.

• PM's US Tour

"All I am saying is that the availability of fissile material has been curtailed," Mishra said in an interview to CNBC for its India Tonight programme.

The India-US agreement requires New Delhi to put two-thirds of its 22 nuclear reactors, as against six at present, under international safeguards, a phenomenon he feared could reduce fissile availability for nuclear deterrence.

• Bush's India Visit

Also, he said the government was required to plan its response to future threats afresh in the light of the new deal.

"We have a no-first-use (nuclear) doctrine, which means the response to any nuclear, chemical attack has to be massive," he remarked and nodded when asked if he believed the pact would impact India's response to such a situtation.

Mishra, who was the national security advisor in the National Democratic Alliance government, however, praised the ruling United Progressive Alliance for the progress in relations with the US.

"I hope there is a shift (in ties with Washington) and hope it is moving forward," he said.

On the whole, he described the nuclear deal as key to India's energy requirements. "We should understand that international cooperation in our civil-nuclear energy cooperation programme is essential. It was necessary. We can't get away with it," Mishra said.