Sri Lankan police have detained 16 more people for questioning overnight, taking the number of arrested since Sunday to at least 76.
An Egyptian, Syrian and several Pakistanis were among those detained for questioning as the police probed deeper into the Easter Sunday bombings.
In a statement, police said one of those detained on Wednesday night was linked to a "terrorist organisation" but gave no other details.
Another person was taken into custody for "spreading and preaching of terrorism" on Facebook.
On Thursday, an explosion occurred in a town east of Colombo, but there were no casualties.
The government has acknowledged its failure to prevent the attacks despite receiving intelligence tip-offs.

13 killed in explosion at Qatar's Ras Laffan LNG site
UK's Starmer resigns, paving way for orderly transfer of power
Fire at coaching centre in India's Lucknow kills at least 15
UK considers forcing social media firms to prioritise trusted news
Temperatures to exceed 40C in European heatwave as three die in France
