SANAA (AFP) - Gunfire and shelling rocked Sanaa for the third straight day on Tuesday as the toll from the worst outbreak of violence in Yemens capital in months spiralled to 60 dead with hundreds wounded. The violence has hampered attempts by regional and international mediators to clinch a power transfer deal between political rivals, with the opposition saying it will not negotiate while blood is flowing in Sanaa. Fighting between dissident military troops and those loyal to President Ali Abdullah Saleh broke out at dawn after a brief lull overnight and raged into the morning, leaving seven people dead, medics and witnesses said. Four civilians and three soldiers from the First Armoured Brigade were killed, a medical official said, referring to Ahmars troops. Sanaa was quiet later on Tuesday as the fighting receded, residents said. Republican Guard troops, commanded by Salehs son, Ahmed, shelled posts held by Ahmars troops around Change Square, epicentre of the anti-regime protests that have shaken Yemen for months, witnesses said. Change Square was targeted by mortar rounds and anti-aircraft fire, with one witness describing it as the heaviest shelling yet and saying it lit the sky over the square. A shell also hit Al-Iman University near the square killing one and wounding three others, said university spokesman Ayed al-Zindani. Mortar rounds struck near the field hospital set up at Change Square and six people were wounded, said activist Walid al-Amari. Snipers and security forces also opened fire on demonstrators who tried to march towards the Kentaky crossroad, where the office of Ahmed Saleh is located. Medics at the Change Square field hospital reported dozens were wounded in the attack but could not yet provide specific figures. Protest organisers told AFP the numbers of demonstrators camped in an area stretching about three kilometres (two miles) from Change Square to Al-Zubair Road had swelled to nearly 150,000. Their figures could not immediately be verified. The latest violence was sparked on Sunday when demonstrators, vowing to escalate their protests, headed out from Change Square, where they have camped since February. They marched southwards along Al-Zubair Road towards Kentaky crossroad in central Sanaa. They were met by security forces and armed civilians who opened fire on them, leaving 26 dead, medics said.