President Maithripala Sirisena has issued a gazette notice banning three Islamic extremist organisations, including National Thowheeth Jama'ath that was blamed for the Easter bombings.
The commander said that by looking at the pattern of operation and the places that the suspects travelled, there has to be some outside involvement of some leadership or instructions.
Silva's name was mentioned in the resolution passed by the UN Human Rights Council (UNHRC) in 2013, alleging rights abuses by the Sri Lankan Army.
The NIA had alerted the island nation that ISIS terrorists were planning to carry out strikes there.
The blockade of Facebook and WhatsApp has been imposed from mid-night following violent incidents between the minority Muslim and majority Sinhalese communities, officials said.