Sri Lankan authorities have ordered a curfew in the capital, Colombo, for a second day on Monday.
It will be in place from 1430 GMT to 2230 GMT on Tuesday, the government information department said.
So far, the police have arrested 24 people and are carrying out searches across the island.
No group has claimed responsibility for the attacks so far.
The Interpol on Monday said it is ready to offer full support to the Sri Lankan authorities in investigating the attack.
This comes as Prime Minister Ranil Wickremesinghe told reporters that some officials had prior intelligence about the attacks but didn't act on it. "This is a matter we need to look into."

Germany, France in rare rebuke of Trump over Iran war
Iran sends missiles into Israel, dismisses Trump's talk of negotiations as 'fake news'
Iran denies talks with US after Trump postpones strikes on power grid
Israeli minister calls for annexation of southern Lebanon
Kim Jong Un says North Korea’s nuclear status is irreversible, threatens South
Japan to start releasing oil from joint stockpiles by end-March, PM says
Death toll nearly doubles to 66 in Colombian military plane crash
Seven overhead power lines out of service due to falling debris in Kuwait
