Three men were detained after they were found suspiciously roaming in the cantonment area near Hisar, police said on Saturday.
A video clip of inside the cantonment area was found in their mobile phones, they said.
Preliminary investigations revealed that a WhatsApp call was also made to Pakistan by one of the suspects in July, police said
The suspects have been identified as Khalid, 22, Mehtab, 28, and Ragib, 34, they said.
All the three are residents of Uttar Pradesh, they added.
Further investigations are underway, police said.