The Sri Lankan government has declared a curfew with immediate effect, and shut down all major social media and messaging services.
"A curfew will be imposed until things settle down," junior defence minister Ruwan Wijewardene told reporters in Colombo.
Government officials said Facebook and WhatsApp have been blocked to prevent misinformation and rumours.
Nearly 140 people have been killed and more than 400 people wounded after eight bomb blasts ripped through churches and hotels in the island nation on Sunday.

Arab ministerial meeting urges action to stop Israeli violations in Jerusalem
Israeli military strikes southern Lebanon
Four people stabbed near London's Covent Garden, woman arrested
US and Iran having 'very good discussions', Trump says
Progressive El-Sayed wins Michigan primary in jolt to Democrats
