The World Council of Churches general secretary, Rev. Olav Fykse Tveit, has condemned an attack on a bus in southern Egypt carrying Coptic Christians.

Militants in military-style uniforms opened fire on a bus carrying Coptic Christians, killing at least 28 people in the latest bloodshed targeting the country's Christian minority, officials said, The Washington Post reported.

The attack took place on as the group was traveling to a monastery on May 26, the Moslem day of prayer, wounding at least 25 people, the Health Ministry said, Reuters news agency reported.

"It is shocking that this attack was directed against people who were on a pilgrimage of peace, and that this attack comes on the heels of ongoing violence and persecution," Tveit said.

He noted, "In the face of this brutality, the human family, all people of faith and of good will, must stand together to recommit to respecting and caring for one another, to protecting one another, and to preventing such violence."

Eyewitnesses described masked men opening fire after stopping the Christians, who were travelling in a bus and other vehicles.

Egyptian television channels showed a smoke-blackened bus evidently raked by gunfire.

There was no immediate claim of responsibility for the attack, which also was on the eve of the Muslim holy month of Ramadan.

The latest attack folows two separate suicide bombings in April on Egyptian churches in the Nile Delta town of Tanta and the country's second city of Alexandria on Palm Sunday, Newsweek reported. Those blasts killed 45 people.

The extremist group callings itself Islamic State, ISIS, or Daesh, claimed responsibility for both attacks.

Following the attacks, ISIS released a statement from a person claiming to be its leader in Egypt, who remains unidentified, in its weekly Al Naba magazine, calling for Muslims to avoid Christian gatherings. The warning suggested that the group planned to target Christians in further attacks.

"We are warning you to stay away from Christian gatherings, as well as the gatherings of the army and the police, and the areas that have political government facilities," the leader said.

Coptic Christians, whose presence in Egypt dates back nearly 2,000 years, to around the time that Jesus lived, account for about 10 percent of Egypt's population of 92 million.

The World Council of Churches said it is appealing to Egyptian President Abdel Fattah al-Sisi, to religious leaders and to governments across the region "to act swiftly and boldly to safeguard the fundamental religious rights of all faiths, to ensure security in the face of violence and to guarantee justice for all people."

Tveit called for prayers, urging the WCC fellowship and others across the world to remain steadfast in their quest for peace and justice for Copts and all who are persecuted.