CAIRO—A senior Egyptian security official says police have seized a ton of explosives headed to the Sinai Peninsula, which borders Israel and the Gaza Strip.

Adel Rifaat, security chief of Suez city at the southern end of the Suez Canal, said Sunday the explosives were discovered in a truck crossing into Sinai from mainland Egypt through a traffic tunnel under the canal.

The truck driver was arrested for questioning about the origin of his cargo and its final destination.

Lawlessness has been rife in Sinai since the ouster of longtime ruler Hosni Mubarak in February 2011. Weapons have flowed into the peninsula from Libya, where an eight-month civil war ended in late 2011. Many of these weapons are smuggled into Hamas-ruled Gaza. Sinai's Islamist militants have also grown in strength.