Gaza, Dec 15 : In response to recent reports that Israel has begun limited flooding of some of Gaza's tunnels with seawater, a Hamas spokesperson said the militant group built the complex underground network system to withstand possible attempts to pump water into them. "The tunnels were built by well-trained and educated engineers who considered all possible attacks from the occupation, including pumping water," CNN quoted spokesperson Osama Hamdan as saying at a news conference in Beirut. "(The tunnels) are an integral part of the resistance, and all consequences and expected attacks have been taken into account," he added. Earlier this week, a US official told CNN that Israel has informed Washington it has started 'carefully testing out' flooding some of Gaza's tunnels with seawater 'on a limited basis' to test the ability to degrade the militant group's underground network on a larger scale. The official however, noted that the Israelis were still unsure of whether it will work. "But they assured the US that they are being careful to only test it in tunnels where they do not believe hostages are being held," he added. On Tuesday night when asked by reporters about the development, US President Joe Biden said: "With regard to the flooding of the tunnels, I'm not at liberty ' well, there is assertions being made that they're quite sure there are no hostages in any of these tunnels, but I don't know that for a fact. 'I do know that, though, every civilian death is an absolute tragedy.' The Israeli military or government have not commented on the report, reports CNN. Earlier this month, Israel's army had said that it destroyed at least 500 tunnel shafts in Gaza and located more than 800 around the Hamas-controlled enclave. The military said last week that many of the tunnel shafts "were located in civilian areas" and inside civilian structures. In 2021, Hamas claimed to have built 500 km worth of tunnels under Gaza, though it is unclear if that figure was accurate or posturing. /IANS