Tel Aviv, Oct 25 : The Israel Defense Forces (IDF), which is planing a major ground offensive in the Gaza Strip, may face a challenge in the form of underground tunnels. Just as the released hostage, 85-year-old Yocheved Lifshitz said, the underground tunnel network is being considered as a major source of support for the Hamas militant group to hide and spring surprises on the advancing IDF troupes. According to an assessment of the IDF, Hamas has a tunnel network of 1,300 tunnels spread across 500 km distance. The military knows that this is one of the largest network of underground tunnels in the world and that this would be the biggest challenge for the forces. Experts believe that the hostages Hamas has taken are being housed in these tunnels which, according to studies conducted are only 2 metres wide and 2 metres high. An Israeli military intelligence report states that these tunnels were constructed initially for smuggling goods from Egypt but after the surveillance increased ,especially aerial surveillance, it led to Hamas using these tunnels to hide its operatives, top leaders as well as to store weapons and food items. The IDF however has 'bunker buster bombs' that can destroy these underground tunnels but the human density in the Gaza Strip, it is difficult to use these bunker buster bombs without affecting civilian population. The Israeli military, according to experts, is well trained in underground warfare and is one of the most capable forces in the world in this mode of war. The IDF has been using special units for this wardare since 2014 trained in simulated tunnels and also learned to use sensors that are specific to understand the structure of the tunnels. The army has also robots that can be deployed inside the tunnels to sense human presence and to act accordingly. /IANS