The police, meanwhile, are trying to decode the contents of a digital diary and a highly-sophisticated wrist-watch seized from the possession of the four persons.

The police have also seized a notebook from the persons, which contains a long list of organisations said to be owing allegiance to the ISI, which includes the United Liberation Front of Assam (ULFA) and some Kashmiri groups.

The ULFA finds mention at no 19 in one particular page of the notebook, along with a radio frequency against it, with Assam Police Inspector-General (Special Branch), N Ramachandran saying the ISI keeps regular contact with the Assam group through this frequency.

The four ISI agents arrested here on Saturday include two ``officers'' MD Fasihullah Hussaini alias Hamid Mehmood (ofSindh) and MD Javed Wakakhar alias MD Mustaffa (of Karachi). The other two are Maulana Hafiz Mohammed Akram Mallik (of Kupwara, Jammu and Kashmir) and Wari Salim Ahmed alias Abdul Aziz (of Mehilki village, Muzaffarnagar, Uttar Pradesh).

According to the police, the hi-tech wrist watch seized from one of them had a cipher with coded messages apart from about 75 phone numbers in its data bank.

The police, meanwhile, is trying to find out the password of the digital diary, while efforts are on to pick up some more local contacts of the arrested persons.

As many as 27 persons from different districts of the state bordering Bangladesh have been already picked up during the past three days, and more arrests are likely to be made in the next few days, police said.

It may be recalled that the four ISI ``officers'' had sneaked into Assam through the porous Indo-Bangla border after flying into Dhaka from Karachi by a PIA flight, in the third week of July.