Fearing an increase in infiltration attempts by terrorists along the border with Egypt, the IDF's Southern Command recently began constructing a barrier along part of the border near the Gaza Strip. The barrier, which includes a fence and barbed wire, is being constructed along a 40-km. stretch between the Kerem Shalom Crossing, at the southwest corner of the Gaza Strip, and the Israeli border town of Nitzana to the south. The border with Egypt, over 200 km. long, is Israel's most porous frontier and is marked only in certain sections by a regular fence lacking electronic sensors. The section being sealed off is used frequently by drug smugglers and refugees to enter Israel. IDF sources said engineering units from the Southern Command's 80th Division have been constructing the barrier and reinforcing existing IDF positions in the area since Operation Cast Lead earlier this year. The sources added that with tightened security along the Gaza border fence, there was concern that Hamas and Islamic Jihad terrorists would step up their efforts to cross into the Sinai Desert and then traverse the porous border with Israel. In addition, there has been concern that other terrorists, including members of Hizbullah cells believed to be in the Sinai, would also try to use this section of the frontier to cross into Israel. "The border with Gaza is basically hermetically sealed," a defense official explained Tuesday. "That is why we are concerned that the terrorists will try to infiltrate via the Egyptian border." A fence along the frontier was first proposed after the disengagement from Gaza in the summer of 2005. With Israel out of the area and deployed tightly along the Gaza border, terror groups decided that the only way to attack Israel was with Kassam rockets - launched at the western Negev - and by sending terrorists to Israel via the Sinai. As a result, security officials began warning of the creation of a "terror triangle" connecting the Gaza Strip, Egypt and Israel.