Updated at 11:42 p.m. ET
A military spokesman said 15 bodies were found in a house where soldiers had pursued suspects in the Easter Sunday bombings. The spokesman said the bodies, including those of six children, were discovered after a shootout in the Eastern province.
A police spokesman said three suspects in the bombings also were killed.
Coordinated bomb attacks at churches and hotels on Sunday killed at least 250 people and left hundreds more wounded.
The U.S. State Department on Friday urged Americans to reconsider travel to Sri Lanka. It also said children of U.S. government employees must leave, and it authorized the departure of nonemergency government employees and their families.
The department warned that terrorists may target public locations such as places of worship, transportation hubs and markets.
Sri Lanka's president says authorities are looking for 140 people with suspected links to Islamic State. Most of those being sought are young people, NPR's Michael Sullivan reports from Colombo; more than 70 people have already been arrested. The shootout erupted on Friday in Sri Lanka's Eastern province as soldiers attempted to raid a building there, with the military and suspects exchanging gunfire.
No Catholic Masses will be held in Sri Lanka this weekend. Archbishop of Colombo Malcolm Ranjith said he had seen a leaked security document that warned of additional attacks on churches, Reuters reports.
"We don't want repetitions," Ranjith said, according to the news service.
Officials urged Muslims to stay home, but many still gathered at mosques for Friday prayers. In Colombo, hundreds of men and boys went to the Masjidus Salam Jumma mosque, where, The Associated Press reports, many prayed through tears.
The mosque's chairman, Akurana Muhandramlage Jamaldeen Mohamed Jayfer, told the AP that the attackers are "not Muslims. This is not Islam. This is an animal. ... We don't have a word [strong enough] to curse them."
Sri Lankan authorities say the suspected leader of the group believed to be behind the attacks was one of the bombers killed on Sunday. Officials say the attacks were perpetrated by National Thowfeek Jamaath, a local militant group associated with ISIS. The group's leader, Mohamed Zahran, died in the attack at the Shangri-La Hotel, one of three hotels targeted by the militants.
On Thursday, the official death count was reduced, to 253 people. Authorities had previously said that more than 350 people had been killed. The discrepancy added to questions about the government's competence.
Parts of the government had been warned that attacks were possibly imminent, but failed to act. That revelation has led to finger-pointing, including from President Maithripala Sirisena, who said that his defense and police chiefs did not share the information with him. Defense Secretary Hemasiri Fernando has resigned.
ISIS has claimed responsibility for the attacks but has not offered proof of its involvement. According to Sri Lanka's deputy defense minister, most of the attackers were "well-educated" and came from "middle class" backgrounds.