The bombings carried out by extremist groups targeted three churches during Easter Sunday services in 2019. Three luxury hotels were also hit in simultaneous attacks on April 21, DPA reported.
Catholic churches conducted prayer services after two minutes of silence in remembrance of the 271 people killed in the multiple explosions. Other religious groups held similar events.
A multi-religious remembrance service attended by Buddhist, Hindu and Muslim clergy and diplomats was held at the St Anthony's Catholic shrine in the capital Colombo - one of the targets of the suicide bombings.
Heavy security was placed outside churches in Colombo and surrounding areas where the main services were conducted.
Silent protests were held outside churches in some locations demanding speedy investigations into the attacks.
"We are not happy about the investigations," head of the Catholic church in Sri Lanka, Cardinal Malcolm Ranjith said, adding that the people need answers about who was responsible and the truth about the motives behind the attacks.
A presidential commission appointed to probe the attacks has concluded its investigation, but Ranjith has claimed that the report fails to fully identify those responsible for the bombings, though it pointed to Islamic extremists groups as the perpetrators.
The commission found former president Maithripala Sirisena responsible for security lapses as he failed to take action on advance warnings about the possible attacks.