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.

US envoys arrive in Qatar as mediators work to revive Iran talks
Afghanistan launches airstrikes on IS targets on border with Pakistan
Bangladesh warns of dengue surge as weather aids spread
Fourteen children killed in Pakistan after tutoring centre roof collapses
Supreme Court rejects Trump bid to restrict birthright citizenship
South Africa's anti-migrant protesters march nationwide
Iran and US agree to halt attacks, uncertainty over Doha talks
Manhunt launched after Monaco blast targets Ukrainian-born oligarch
