Masked gunmen opened fire on a bus carrying Coptic Christians in Egypt on Friday, killing at least 26 people, according to The Associated Press.
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Another 25 people were wounded in the attack, which took place south of Cairo, Egypt's ministry of interior told the AP.
No group immediately claimed responsibility.
Last month, ISIS claimed responsibility for attacks on Coptic churches in northern Egypt on Palm Sunday in which 49 people were killed.
Coptic Christians make up just 10 percent of Egypt's population of 92 million.
Egypt responded to Friday's attack by launching airstrikes against what it said were militant training bases in eastern Libya, according to the AP. The bases targeted are associated with the Shura Council, an Islamist militia known to be linked to al-Qaeda. Egypt's president, Abdel Fattah el-Sisi, announced the retaliatory actions hours after the attack.
U.S. President Donald Trump condemned the attacks and said the United States stands in solidarity with Egypt.
"Terrorists are engaged in a war against civilization, and it is up to all who value life to confront and defeat this evil," Trump said Friday. "This merciless slaughter of Christians in Egypt tears at our hearts and grieves our souls. Wherever innocent blood is spilled, a wound is inflicted upon humanity."
Trump said the attack "steels our resolve to bring nations together for the righteous purpose of crushing the evil organization of terror, and exposing their depraved, twisted and thuggish ideology."
ABC News' Julia Jacobo and Jordyn Phelps contributed to this report