For the first time since disengagement, troops entered the Gaza Strip near the Kissufim crossing on Thursday in search of bombs they feared had been planted along the security fence. On Wednesday night, as most of the country was sitting down to the Pessah Seder, two terrorists armed with grenades and automatic rifles were killed as they tried to infiltrate into Israel. Led by Col. Moni Katz - commander of the Northern Gaza Brigade - the troops from an engineering unit made a brief incursion 50 meters into Gaza on Thursday and after several hours left after verifying that no bombs had been planted along the fence. Interim Prime Minister Ehud Olmert's decision to cut off ties with the Palestinian Authority and, as a result, coordination with PA security forces was what led to the decision to enter Gaza, a source in the Southern Command said. "We cannot coordinate with nor rely on the PA security forces to search for bombs as we did in the past," one officer explained. "So now we have no choice but to go in and search for ourselves." But while troops have already begun training in the Golan Heights for a possible future extensive incursion into Gaza, the officer stressed that Thursday's raid was purely defensive and not offensive. "When there is danger to our troops, we will take action," he declared. The officer said that the army was prepared to invade Gaza if ordered to do so by Olmert. "We are ready for any scenario," he said. "And it could be that in the future we will invade Gaza." The attempted infiltration occurred Wednesday night after two terrorists were spotted by soldiers crawling along the security fence near the Kissufim Crossing. Tanks and helicopters opened fire and the two - later identified as members of the Aksa Martyrs Brigades - were killed. Two Kassam rockets were also fired over the holiday. In response, IDF artillery pounded Kassam launch sites in the northern Gaza Strip. IAF aircraft also bombed a building in Gaza City that was used as an Aksa Martyrs Brigades headquarters Tuesday night. No one was wounded. The IDF said the building was used to plan terror attacks and served as a recruitment center. Meanwhile Wednesday, soldiers from the Nahal Brigade discovered 30 kilograms of explosives belonging to Islamic Jihad in a weapons laboratory near Jenin. The army said that the explosives were found "ready for use." Sappers blew up the laboratory.