Catholics in the Sri Lankan cities of Colombo and Negombo, where churches were targeted by suicide bombers on Easter Sunday, have held their first Sunday morning masses since the attacks that killed more than 250 people.

Police stood guard at every entrance to St Lucia’s cathedral in Colombo, one of the country’s largest churches, which was full of worshippers, including many who lost relatives in the bombings on 21 April claimed by Islamic State.

Those attending underwent full-body searches and were banned from bringing bags, and the road outside was barricaded and guarded by soldiers. Troops wearing masks and camouflage clothing patrolled the surrounding area on motorbikes.

Soldiers stand guard at St Lucia’s cathedral. Photograph: Lakruwan Wanniarachchi/AFP/Getty

Joshua Berney, eight, found it too much, and left partway through the mass. His aunt, an uncle and three cousins – one of whom was his best friend – were killed at St Anthony’s church in Colombo.

His mother, BJ, said: “We still haven’t found his body, so it’s difficult. My son finds it tough.”

At Mother of Seven Sorrows Mater Dolorosa church, two streets away from St Anthony’s, devotees trickled in until the building was full. Wall-mounted fans whirred at capacity to beat back the intense humidity.

Fr Fernando Marcelliar, who led the service, said: “The parishioners were really upset that we didn’t have a mass the last two weeks.” He held a private mass last Sunday, which about 50 people heard about and attended.

“Others found out later that there was a mass and they couldn’t come, and they were really upset – they even scolded me,” Marcelliar said.

A priest gives an emotional address to worshippers at St Theresa’s church. Photograph: Dinuka Liyanawatte/Reuters

More than a dozen children in the congregation were having counselling, he said. “One mother told me yesterday that her son of eight years gets excited even by the slightest noise and doesn’t sleep well at night,” Marcelliar said.

Stephan Fernando, 16, was apprehensive as he entered the mass. He was serving as an altar boy at St Anthony’s when a suicide bomber detonated a device inside. “I feel better now that I’ve received communion,” he said after the service.

His brother, Eugine, who was also serving the altar that Sunday, had decided to stay at home and had been avoiding public places.

In tears, their mother, Sharmila, said: “My children are OK, but [the victims] were also someone’s children, who were loved and cared for.

“I saw how my sons’ shirts were splattered with the flesh and blood of others when they were coming out. I didn’t see the church, but I could understand how bad the damage was.”

The masses in the two cities – services elsewhere in the country had restarted earlier – were small steps towards the resumption of normal life after the attacks that ended a decade of relative peace following the government’s brutal victory in the country’s 27-year civil war against Tamil militants.

Students at state-run schools resumed classes last week. Campuses were guarded by police, and parents asked to replace school bags with clear plastic sacks. Attendance remains low.

Catholic private schools, which have been shut since the attacks, are likely to reopen on Tuesday.

A heavy police and army presence is still visible in major cities and villages as security forces continue the hunt for accomplices of the terror cell that carried out the bombings.

The president of Sri Lanka, Maithripala Sirisena, told parliament most of the 150 people suspected to have been linked to the plot have died or been arrested. He said 56 had been arrested on suspicion of direct involvement in the plot, of which 12 were hardcore terrorists.

The precise involvement of Isis in the attacks is not clear. Sirisena said police had so far discovered 13 safe-houses, 41 bank accounts and 19 vehicles and motorcycles belonging to the bombers. Those who aided the terrorists had been paid cash rewards of up to 2 million rupees (£8,700), he added.

Police are continuing to issue specific warnings of possible attacks in Colombo.