Protesters have been stoning security forces in Cairo on the third day of unrest in the Egyptian capital over the military government.Ten people are now known to have been killed and hundreds injured since the trouble began on Friday.It has emerged that precious national archives were burnt when the Institute of Egypt was set alight.The violence has overshadowed the first parliamentary elections since President Hosni Mubarak was ousted in February.The latest unrest has highlighted divisions in Egyptian society, the BBC's Yolande Knell reports from the city.While some activists are angry at the army's seeming reluctance to give up power, there are many people who support it as a stabilising force during this difficult period of political transition, she says.The latest round of voting in the election for a new parliament passed off peacefully, with more gains for Islamist parties.Hundreds of protesters have camped out in the cold on the city's Tahrir Square.Shortly before dawn, soldiers advanced from the barriers they had erected on streets adjoining the square and the confrontations restarted.But this was not a repeat of the violence seen earlier when some protesters were beaten to the ground with sticks and shots were fired at them, our correspondent says.The Institute of Egypt was set on fire two days ago and the building is still smouldering.It had housed national archives going back over two centuries and its paper archives have now been largely been destroyed.Some burnt papers can be seen on the streets, our correspondent says.Egyptian television talk shows have focused on the loss of national heritage.In another development, an Egyptian natural gas pipeline to Israel and Jordan was attacked again on Sunday morning.No fire broke out because the line through North Sinai was already disabled, a security source was quoted as saying by Reuters news agency.