(CNN) -- Gunmen opened fire on an army bus in Cairo Thursday, killing one officer and injuring three soldiers, Egypt's state-run EgyNews reported.
Islamist militants are expanding their insurgency in Egypt where army chief Field Marshal Abdel Fattah El-Sisi, who overthrew former president Mohamed Morsy of the Muslim Brotherhood last July, is expected to announce he will run for president.
Militants based in the Sinai peninsula near the Israeli border have stepped up attacks on soldiers and policemen since Morsy's ouster which came amid widespread protests against his rule. Morsy and other Brotherhood leaders were rounded up soon after.
CNN's Marie-Louise Gumuchian contributed to this report