AL JAZEERA (Qatar), HAARETZ (Israel), CNN (USA)
Egyptian army Apache helicopters fired rockets at armed militants near the port town of El Arish.
"Over 48 hours since that audacious and shocking attack on the Egyptian military post here in Sinai, it seems that the army has decided to hit back," said Al Jazeera reporter Jamal Elshayyal.
It is the first time that the Egyptian air force has been called into action in Sinai since 1973, adds Israeli newspaper Haaretz.
This clash comes less than three days after a previous attack in Sinai which killed 16 Egyptian gunmen as a group of terrorists tried to force its way through the border in Rafah, which is the only crossing into Gaza not controlled by Israel.
No group has yet claimed responsibility for the initial Sinai attack, reports Al Jazeera.
According to the Qatari news channel, Egypt and Israel say both Islamist fighters from the Sinai and Palestinian allies from the Gaza Strip are active in northern Sinai.
Egypt has begun to seal off smuggling tunnels into the Gaza Strip.