Hamas is trying to establish a bunker system as well as fortified rocket-launching and surveillance positions along the security fence with the Gaza Strip, Brig.-Gen. Moshe (Chico) Tamir, head of the Gaza Division, said Monday. Tamir said that Hamas was "building an army" in the Gaza Strip and had obtained unprecedented capabilities through smuggling tunnels between Gaza and Egypt. On Monday, head of the Shin Bet (Israel Security Agency) Yuval Diskin said that since Israel's withdrawal from Gaza in 2005, the Palestinians have smuggled over 112 tons of explosives into the Strip. "They are trying to dig tunnels, build surveillance positions and mortar-fire stations along the fence," Tamir told reporters during a briefing concerning the death of IDF reservist Ehud Efrati during clashes with Hamas gunmen early Monday morning. "They are trying to build this up and we are trying to stop them." Tamir said that Hamas was studying Israeli tactics during the IDF's daily operations along the fence and was trying to use this knowledge in its fighting methods. "This is ongoing warfare and as such there is also a simultaneous brain war taking place," he said. "We are always studying what we do and modifying our tactics. They are trying to study us and to be wise with that knowledge." Tamir said that for the IDF's current purposes there was no point in expanding the operations deeper into Gaza. He also said that while the IDF was working to reduce the Kassam fire from Gaza there was no perfect solution. "They can fire Kassams from one edge of Gaza all the way to the other and farther," he explained. "We are operating close to the fence since that is where they fire mortar shells, anti-tank missiles and dig tunnels." Also on Monday, senior Hamas official Nizar Riyan said Hamas will overthrow Fatah and takeover the West Bank in less than a year. "Next fall we shall pray in Ramallah," Israel Radio on Monday evening quoted Riyan as saying during a rally in the Gaza Strip refugee camp of Jabaliya. senior PLO official Yasser Abed Rabbo said in response that Riyan should be "admitted to a mental institution."