American engineers who serve as consultants for the Egyptian military have recently informed Israel that Hamas has succeeded in digging 60-meter deep smuggling tunnels to avoid detection and destruction by the IDF, defense officials said on Thursday. The American engineers, deployed as consultants along the Philadelphi Corridor in Egyptian Rafah, have been using technology that can detect seismic movements to uncover tunnels. But it is more difficult to detect them once they have reached the 60-meter depth, the engineers told their Israeli counterparts. According to IDF assessments, Hamas now has several hundred active tunnels under the Philadelphi Corridor, even though close to 300 were reportedly bombed by the Israel Air Force during Operation Cast Lead in December and January. Digging to the new depths required special techniques, one official said. "The Palestinians are experts at digging tunnels," the official said. "They reach 60 meters, pump out the groundwater, and pump in air so they can continue digging." Defense officials said that since Cast Lead, Cairo had increased its efforts to uncover and destroy smuggling tunnels. The Egyptian efforts have also focused on stopping weapons before they reach the Philadelphi Corridor and as they make their way to the border with Sinai. A senior IDF officer said the army was reassessing the effectiveness of bombing tunnels from the air. "We found that it takes the Palestinians just a few days to rebuild the tunnels after we bomb them," the officer said. According to a recent report on Al-Arabiya TV, the tunnel-smuggling industry in Gaza is valued at $200 million annually, yielding huge profits for the Palestinian and Egyptian owners of the tunnels. There are 800 tunnels along the Gaza-Egyptian border, Al-Arabiya said. "These tunnels are the lifeline of the Gaza Strip. This is the only place where you don't feel you are in a besieged city. All products are available - electronic appliances, flour, sugar and all other food products - and even diapers and Viagra pills," according to a transcript of the TV report provided by MEMRI: The Middle East Media Research Institute.