CAIRO (AP) — Masked militants riding in three SUVs opened fire Friday on a bus packed with Coptic Christians, including many children, south of the Egyptian capital, killing at least 28 and wounding 25, the Interior Ministry said.

No group immediately claimed responsibility for the attack, the fourth to target Christians since December, but it bore the hallmarks of the Islamic State group.

Islamic militants have for years been waging an insurgency mostly centered in the restive northern part of Egypt’s Sinai Peninsula, although a growing number of attacks have recently also taken place on the mainland.

The assault happened while the bus was traveling on a side road in the desert leading to the remote monastery of Saint Samuel the Confessor in Maghagha, in Minya governorate, about 220 kilometers (140 miles) south of Cairo.

Security officials quoted witnesses as saying they saw between eight and 10 attackers, dressed in military uniforms and wearing masks. The victims were en route from the nearby province of Beni Suef to visit the monastery.

Khaled Mogahed, the Health Ministry spokesman, said the death toll stood at 26 but feared it could rise further. According to Copts United news portal, only three children survived the attack. It was not immediately known if most or all of the victims were children.

Arab TV stations showed images of a badly damaged bus along a roadside, many of its windows shattered. Ambulances were parked around it as bodies lay on the ground, covered with black plastic sheets.

President Abdel-Fattah el-Sissi called for a meeting with top aides to discuss the attack.

In April, twin suicide bombings struck two churches north of Cairo on Palm Sunday, and in December, a suicide bombing targeted a Cairo church. The attacks left at least 75 dead and scores wounded. IS claimed responsibility and vowed more attacks.

Late last month, Pope Francis visited Egypt, in part to show his support for Christians in this Muslim majority Arab nation who have been increasingly targeted by Islamic militants. During the trip, Francis paid tribute to the victims of the December bombing at Cairo’s St. Peter’s church, located in close proximity to Cairo’s St. Mark’s cathedral, the seat of the Coptic Orthodox Church.

Following the pope’s visit, IS vowed to escalate attacks against Christians, urging Muslims to steer clear of Christian gatherings and Western embassies, saying they are targets for the group’s followers.

Egypt’s Copts, the Middle East’s largest Christian community, have repeatedly complained of discrimination, as well as outright attacks, at the hands of the country’s majority Muslim population. They account for about 10 percent of Egypt’s 93 million people.

They rallied el-Sissi, a general-turned-president, when he in 2013 ousted his Islamist predecessor Mohammed Morsi, who hails from the Muslim Brotherhood group. Attacks on Christian homes, businesses and churches subsequently surged, especially in the country’s south, the heartland of Egypt’s Christians.