Masked gunmen opened fire on an army bus in Cairo on Thursday, killing one officer and wounding three soldiers, a military source told Reuters.
Islamist militants are expanding their insurgency in Egypt where army chief Field Marshal Abdel Fattah al-Sisi, who overthrew Mohamed Morsi of the Muslim Brotherhood in July, is expected to announce he will run for president within days.
The army quickly blamed the Muslim Brotherhood for the attack.
"Masked armed men belonging to the terrorist Brotherhood targeted a bus of the armed forces... which led to the martyrdom of the Warrant Officer Yusri Mahmoud Mohamed Hassan," the army spokesman said in a statement on Facebook.
Militants based in the Sinai peninsula near the Israeli border have stepped up attacks on soldiers and policemen since Morsi's ouster, killing hundreds and spreading their campaign to Cairo and other cities.
A security crackdown has devastated the Brotherhood, driving Egypt's most organized political group underground.
But Sinai-based militants are still a major security threat to the Arab world's biggest nation despite army offensives which include air strikes.