SIRTE, Libya - Libyan government forces fired rounds of heavy artillery at Muammar Gaddafi's home town of Sirte on Friday as they launched their largest assault so far to capture the last major bastion of support for the deposed leader. Taking the coastal town would be an important symbolic trophy for Libya's new rulers, and would bring them closer to finally gaining control of the whole country almost two months since their fighters seized the capital Tripoli. Forces loyal to the ruling National Transitional Council (NTC) are under pressure to intensify their advance but heavy resistance and gunfire by Gaddafi loyalists have prevented them from taking the city for weeks. Columns of black smoke rose above Sirte's skyline as NTC forces fired tank shells and rounds of artillery toward the city centre from their positions to the east of Sirte. Thousands of civilians have fled Sirte as fighting intensified, describing an increasingly desperate humanitarian situation. Many were caught off guard by Friday's assault and fled in panic as explosions boomed around the city. “There are strong strikes in all directions. Today we will finish it. God willing today we will capture Sirte,” said Colonel Ahmed El-Obeidi, an NTC commander. NTC lorries with ammunition and artillery batteries were brought forward to the eastern front line, about 1.2 kilometres (0.8 miles) away from the city centre. Along with the desert town of Bani Walid, Sirte is one of the last strongholds still controlled by Gaddafi loyalists. Doctors at a field hospital east of Sirte said they heard a huge explosion inside the city after midnight. Colonel Obeidi said the explosion occurred after his forces hit a weapons storage facility belonging to Gaddafi supporters. Gaddafi loyalists who pulled back to Sirte when they lost control of other cities are putting up fierce resistance. They have been mainly using sniper fire and rocket-propelled grenades to prevent NTC forces from entering the city centre. The prolonged fighting has raised concerns about civilians in the coastal city of 75,000 people. At a field hospital several kilometres west of Sirte dozens of ambulances brought in at least 50 fighters and civilians wounded in the fighting. Most were seriously wounded. Medical workers tried to save an unresponsive woman. A child with a wounded leg sat on the floor. A helicopter landed near the hospital to carry some of the wounded to hospitals in Misrata, which lies west of Sirte.