Two Egyptian soldiers were killed and four were injured on Thursday when gunmen opened fire on a military checkpoint near the North Sinai town of Sheikh Zuweid, security and medical sources told Reuters.
Militants also attacked four other army sites in Sheikh Zuweid, which lies near Egypt's border with Israel and the Palestinian Gaza Strip, injuring at least three soldiers.
Egypt's lawless Sinai peninsula has seen a spike in violence since the army ousted the country's Islamist president on July 3.
In separate attacks in Sinai on Wednesday, two soldiers were killed in a gun battle and four militants died when their explosives-laden car detonated near a police base.
Medical sources said around 20 policemen and soldiers have been killed in Sinai since president Mohamed Mursi's exit.
Army sources estimate there are around 1,000 armed militants in Sinai, many of them members of local nomadic tribes, divided into different groups with varying ideologies or clan loyalties, and hard to track in the harsh terrain.
Some want to establish Islamic law in Egypt, and are likely to have been incensed by Mursi's removal. Weapons are flowing in, especially from Libya, and a number of the groups are thought to have links with al Qaeda.
Reporting by Yusri Mohamed; writing by Shadia Nasralla; Editing by Noah Browning and Alison Williams