A senior Egyptian security official says police have discovered 20 underground tunnels and seized thousands of gallons of fuel being smuggled under the Egypt-Gaza border.

He says four smugglers were arrested early Thursday after a heavy exchange of gunfire with Egyptian forces. Three of the suspects and one policeman were injured.

The official says the suspects were laying an 800-meter underground pipeline to ship fuel illegally into Gaza. He spoke on condition of anonymity because he was not authorized to talk to media.

He says the tunnels were uncovered over the past week. Fuel and supplies are often scarce in Gaza, whose borders are frequently shut because of security concerns.