Three monks belonging to Egypt's Coptic Orthodox Church were killed in an attack at a monastery in South Africa on Tuesday, the church said.

They were killed at the Saint Mark the Apostle and Saint Samuel the Confessor Monastery. The Coptic Orthodox Church, which is based in Egypt, named the monks as Monk Hegumen Takla el-Samuely, Monk Yostos ava Markos and Monk Mina ava Markos. All three were Egyptian nationals.

The Coptic Orthodox Church of South Africa said that el-Samuely was the deputy of the South African diocese.

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Police said they were investigating a murder case and that the motive for the attack was not known. A police spokesperson didn't immediately respond to a request for comment, but police told the South African news website News24 that the three monks were stabbed.

A fourth was injured after being beaten with an iron bar, News24 said, quoting police Col. Dimakatso Nevhuhulwi.

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The Coptic Orthodox Church of South Africa said the monks were the victims of "a criminal attack," which resulted in their "martyrdom."

The Egyptian ambassador to South Africa visited the monastery following the attack, it said.

The Coptic church is one of the oldest Christian communities in the world. The church has been the target of deadly attacks by Islamic militants in Egypt and elsewhere.