Egyptian police have discovered 20 underground tunnels and seized thousands of gallons of fuel being smuggled under the Egypt-Gaza border, a senior Egyptian security official said Thursday. He said 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 said the suspects were laying an 800-meter underground pipeline to ship fuel illegally into Gaza. He spoke on condition of anonymity as he was not authorized to talk to media. He said the tunnels were uncovered over the past week.