By MOHAMMED DARAGHMEHRAFAH, Gaza Strip (AP) â¿¿ Rafah's biggest industry is back in business: Gazans are rebuilding the network of underground smuggling tunnels crisscrossing the Egyptian border that were pummeled in a recent Israeli offensive, restoring the illicit conduit for consumer goods and weapons so crucial to Hamas rule. The 12-kilometer (eight-mile) slice of land at the Gaza Strip's southern tip is humming around the clock with workers carting in cement, bricks, gravel and scaffolding. The quick rebound has raised questions about how much damage Israel inflicted on the tunnels during last month's eight-day air offensive. Anwar Abu Lebdeh and seven other workers were laying bricks on a recent day to rebuild the entrance to a 500-meter (550-yard) tunnel battered by an Israeli airstrike last month. Nearby, workers hauled cement sacks on their shoulders, and a bulldozer lifted gravel onto a nearby truck. After loading up at tunnel sites, trucks lumbered over to Hamas government points to pay taxes on their cargo. "It's our source of life, this is the only job we could find. I have been working here for five years," said Abu Lebdeh, 24, who had to slog through mud left by heavy rain to get the job done. The tunnel industry has become key to Gaza's economy since Israel and Egypt imposed a blockade on the territory after Hamas seized power there in 2007. The tunnels ferry in a wide range of items besides essentials, including Chinese motorcycles, farm and zoo animals, appliances â¿¿ and large Iranian rockets that can hit Tel Aviv. Responding to months of daily rocket salvos from Gaza, last month Israel unleashed its air force, starting with an airstrike that killed Hamas commander Ahmed Jabari. In eight days, the Israeli military carried out more than 1,500 airstrikes on militant targets, including rocket-launching sites, weapons storehouses and dozens of the roughly 500 smuggling tunnels operating under the short border.