Libyan leader Moamer Kadhafi said on Saturday he would never leave the land of his ancestors after fresh international calls for him to go and as rebels pressed their campaign to overthrow him. "They are asking me to leave. That's a laugh. I will never leave the land of my ancestors or the people who have sacrificed themselves for me," he said in a loudspeaker address to supporters in Zawiyah, some 50 kilometres (30 miles) west of Tripoli. Western and regional powers met in Istanbul on Friday for the fourth gathering of the Libya contact group, which saw a new call on Kadhafi to go after more than four decades in power. "I'm ready to sacrifice myself for my people, and I will never quit this land sprinkled with the blood of my ancestors who fought Italian and British colonialists," he said of the five-month-long revolt against his rule. "These rats have taken our people hostage in Benghazi, Misrata and the western mountains, using them as human shields," Kadhafi said of insurgents in the rebel capital in the east and port city in the west. "Five million armed Libyans will march on them and liberate the occupied towns as soon as the order is given," he added. In the east, rebels said their steady advance on the key oil hub of Brega was hampered Saturday by the discovery of defensive trenches around the city that had been filled with flammable chemicals by retreating Kadhafi troops. After a small rebel reconnaissance unit from the north punched through to Brega late on Friday before falling back, a rebel commander said troops were also moving "slowly but surely" towards the town from the south and the east. By late on Saturday the rebels were positioned around four kilometres from Brega in their northern approach and within eyesight of the town coming from due east. "We are advancing and we are very close to Brega," said Mustafa al-Sagezli, a member of the rebel's revolutionary military council, adding that Kadhafi's troops had fallen back to positions inside the town. But the commander said landmines and a series of booby-trapped trenches had forced them to slow the attack. "We know Kadhafi's forces have installed a lot of mines. They have even dug holes and trenches (filled) with some chemical liquids and oil to fire them when our forces enter Brega," he said. It was not clear what kind of chemicals were being used, but Brega is home to a large petrochemical facility that produces a range of oil by-products. Libya's largely volunteer rebel army began its push on Brega late on Thursday, hoping to oust an estimated 3,000 loyalist fighters and provide a morale boost for war-weary rebel supporters. "Most of Kadhafi's troops seem to be at the centre," said rebel military spokesman Mohammed Zawi. But the rebel assault took its toll, with at least 12 dead and 178 wounded after bloodiest day yet since the offensive began, according to medics. At a hospital in Ajdabiya, Dr Ahmed Dinari said many casualties were caused by landmines rather than heavy artillery. "We have had five more injuries this morning, all of them from mine explosions," he said. Lying prone in "Bed 2," 19-year-old Ali Saleh said he had been in the central rebel column when his armoured personnel carrier hit a mine. "We were very close to Brega at around three in the morning. Then we got instructions from NATO to fall back and as we were falling back the vehicle hit a mine, destroying the chain track." He was suffering from shock and a lightly damaged knee. Sagezli said 250 mines had been uncovered so far. South of Brega, where the rebels made initial gains but took many casualties, Kadhafi forces wounded many fighters with rocket fire before NATO warplanes carried out air strikes overnight. The alliance said on Friday it hit one tank, a multiple rocket launcher, five armoured vehicles and seven armed vehicles around the town. In raids near Tripoli, NATO aircraft also took out a radar facility and a surface-to-air missile launcher. Southwest of the capital, a rebel checkpoint commander said Kadhafi troops had fired five missiles at their forces who responded with rockets. "There has been no fighting in the valley (near Gualish); it is quiet. Kadhafi's forces have carried out several operations but they are sufficiently far from us not to pose any problems," Shaban Aaboz said. Another commander said rebel forces were still positioned near Asabah, 80 kilometres (50 miles) south of Tripoli and the last obstacle between rebels and the garrison town of Gharyan. "The position is secure; we are discussing with Asabah people how civilians can get out of town before we launch an assault," said commander Mokhtar Lakhdar.