The Golani Brigade troops approached the target quietly and cautiously. Intelligence indicated that the two-story home they were surrounding on the outskirts of Gaza City's Saja'iya neighborhood was being used as a Hamas command center. As the infantrymen closed in, Hamas gunmen popped out of two tunnels directly beneath the home. The troops opened fire and killed them. The clash was just one of dozens that have taken place inside the northern Gaza Strip since four IDF infantry and armored brigades swept in on Saturday night and began the second phase of Operation Cast Lead. According to Palestinian sources, Israeli units have taken up positions in Sajaya, Beit Lahiya, Jabalya and al-Atatra, which are being scoured for Hamas gunmen and infrastructure. Soldiers with camouflaged faces and night-vision goggles have established emplacements inside homes, often changing places so as not to become static targets. Troops moving through fields and orchards are being led by dogs from the IDF's Oketz K-9 unit that are trained to sniff out booby-traps. There has been fierce resistance from well-entrenched gunmen, with anti-tank missiles, mortar barrages, heavy machine gun fire and roadside bombs being just some of the challenges to the IDF. While the army has denied Arab media reports that Hamas had kidnapped an Israeli soldier, IDF sources said that commanders in the field had been instructed to take extra precautions. Throughout Sunday, Apache Longbow attack helicopters, called Saraf by the IAF, could be seen hovering over the Gaza Strip alongside small drones. Every few minutes, the helicopters released flares to confuse heat-seeking shoulder-launched anti-aircraft missiles Hamas is believed to have smuggled into the area. The IDF has cut off the northern Gaza Strip from the south to impair Hamas's ability to send reinforcements and supplies. The group is believed to have an army of close to 20,000. Troop movements in northern Gaza are being accompanied by heavy artillery support from batteries deployed along the border. One soldier from the Reshef Battalion said he had fired close to 200 artillery shells into open areas near Sajaya in support of the Golani Brigade. Artillery officers accompanying infantry units inside Gaza are providing them with targets. Some of their shells have messages scrawled on them: "Address: Hamas" and "To Ja'abri with love," a reference to Hamas's military commander and so-called chief of staff, Ahmed Ja'abri. The brigade commanders inside Gaza include colonels Herzi Levy of the Paratroop Brigade, Ilan Malka of the Givati Brigade and Yossi Peled of the Golani Brigade. The commander of the Gaza Division, Brig.-Gen. Eyal Eizenberg, has also been inside Gaza. The overall commander of the operation is OC Southern Command Maj.-Gen. Yoav Galant. His deputy is Brig.-Gen. Harel Knafo. Maj.-Gen. (res.) Yom-Tov Samia, a former OC Southern Command, is serving as a personal adviser to Galant. Several branches are represented beneath the senior command, including an officer responsible for the coordination of air strikes, an officer responsible for the planning of operations, and a third officer, former Gaza Division commander Brig.-Gen. Moshe "Chico" Tamir.