The number of victims in the blast may increase, the official said.
An officer and ten conscripts were killed and two others injured in North Sinai's Sheikh Zuwayed after a improvised explosive device exploded, the official said.
Another security official said that the preliminary investigations show that Ansar Bait el-Maqdes, the dominant Militant group in Sinai, is responsible for the attack.
North Sinai has witnessed many violent attacks by militants since the January 2011 revolution that toppled the ex-president Hosni Mubarak government.
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About 1,400 people have died in violence since Morsi's overthrow. At least 700 of his supporters were killed in a single day on August 14 last year.
Many policemen and soldiers have been killed in the attacks. In July, militants attacked a military checkpoint in Al-Wadi Al-Gedid governorate in southern Egypt, killing 21 Egyptian border guards and injured four others.
The guards were killed during an exchange of fire with the unknown gunmen which led to an explosion at the checkpoint's ammunition storage.