The Islamic State has imposed a new alarming reality and challenge on authorities in Egypt following the deadly bombing of a church in Cairo. By claiming responsibility for the Dec. 11 bombing of Saint Mark's Cathedral, the seat of Egypt's Orthodox Christian Church and home to the office of its spiritual leader, Pope Tawadros II, IS is waging its war against Egypt directly, not through its local branch, known as Sinai Province. "This is clear from the statement issued by ISIS following the church bombing," said Kamal Habib, an expert on Islamist groups. "It is the mother organization that is talking this time, not its Egyptian branch." The church bombing left 24 women and a child dead and close to 50 people injured. It was the first time IS directly targeted the Christian minority inside Egypt, dealing a strong blow to President Abdel Fattah al-Sisi, who had taken personal responsibility for protecting them. The challenge for Egypt, terrorism experts said, will be to control its internal security situation with the return of hundreds — possibly thousands — of Egyptians fighting within the ranks of IS in Iraq, Syria and Libya as the radical organization loses ground in those countries. A large number of Egyptians have traveled to Turkey and then in Syria and Iraq to join IS, according to Egyptian security agencies. Some Egyptians left for Libya during and after Islamist President Muhammad Morsi ruled Egypt in 2012-13. "Their return will be catastrophic to our country," Habib said. "They can stage painful attacks everywhere in Egypt." Hardened by years of fighting, returning militants will not be easy for Egyptian security agencies to stop, other experts said. The Egyptian Interior Ministry refused to answer questions on the measures it is taking to track down returning militants but, according to media reports, the ministry is reviewing the files of Egyptians who returned from Turkey, Jordan, Lebanon and Iraq in recent months. Some militants are reported to have sneaked into Egypt from Libya. Foreign militants are said to have masqueraded as tourists, entered Egypt and then joined Sinai Province. The Interior Ministry did not confirm such reports. Fouad Allam, a former senior official with Egypt's State Security, the country's internal intelligence agency, said security agencies have received information about the return of militants from Syria and Iraq. "Tighter measures have been taken at entry points to track them down and arrest them," Allam said. "There is information already that ISIS will send some elements to carry out attacks here."