Islamabad, May 31 (IANS) A Pakistani journalist who went missing Sunday after a story on the terrorist attack on a navy base is in the custody of Pakistan's spy agency ISI, a rights body has alleged.

The well-informed Saleem Shahzad, who writes extensively on Islamist groups for Asia Times Online, disappeared after leaving his home to take part in a television talk show.

Those close to Shahzad told the Daily Times newspaper that he had earlier received warnings from security agencies for his reporting on Pakistan, in particular the activities of militant groups.

They feel that his reports on the May 22 terror attack at a key naval base in Karachi may have led to his abduction.

Terrorists stormed the PNS Mehran base and destroyed two surveillance aircraft. The siege ended after 16 hours of fighting that left 10 security personnel and four terrorists dead.

Human Rights Watch (HRW) said it had learnt that Shahzad was in the custody of the Inter-Services Intelligence (ISI).

HRW's Pakistan representative Ali Dayan Hasan told Daily Times Monday that they had documented similar cases of abduction and torture of journalists by security agencies.

Those close to Shahzad told the daily that he was picked up by intelligence officials who have apparently promised to release him soon.

Shahzad was taken away by unidentified people Sunday evening when he left his F-8 Sector residence.

His mobile phone has been switched off since then. There is also no trace of his car.