Pakistan and India on Tuesday exchanged lists of their nuclear sites under an agreement between the South Asian rivals to swap such information annually on New Year's Day, the foreign ministry said.
The information was exchanged under a 1988 agreement on the prohibition of attacks on each other's nuclear installations, a ministry statement said.
Pakistan has sparked international concern that its nuclear weapons could fall into the wrong hands amid months of political turmoil, which peaked, with the December 27 assassination of opposition leader Benazir Bhutto.
"The government of Pakistan and India on Tuesday exchanged lists of their respective nuclear installations and facilities," the Pakistani foreign ministry statement said.
Officials handed over the lists at each other's foreign ministries in New Delhi and Islamabad, it said. Mostly Muslim Pakistan and mainly Hindu India have fought three wars since independence from Britain 61 years ago and conducted tit-for-tat nuclear tests in 1998.
The agreement on handing over details of their atomic facilities came into force in 1991 and the first exchange was on January 1, 1992.
The rivals launched a slow-moving peace process in January 2004 after coming close to another war two years earlier over the disputed Himalayan state of Kashmir.
In October 2005 they formalised an agreement on pre-notification of ballistic missile tests. They have also set up a telephone hotline aimed at preventing accidental nuclear conflict.