Sudanese security forces fired tear gas on Thursday aiming to stop thousands of protesters demanding a transition to civilian rule, the latest rallies in weeks of unrest since a military coup. Singing, beating drums, and holding up posters of some of the dozens killed in demonstrations since the October 25 putsch, protesters in the capital Khartoum shouted defiant slogans against the army.Many protesters in Khartoum were seen wounded and struggling with breathing difficulties due to the heavy firing of tear gas, according to the witnesses. The military takeover — one of several in Sudan’s post-independence history — has seen security forces launch a crackdown that has left at least 57 people dead and hundreds wounded, according to the independent Doctors’ Committee, part of the pro-democracy movement. “We will not stop until we get our country back,” shouted one protester, 22-year old Samar al-Tayeb. Other demonstrators set fire to tyres to create burning barricades on the streets.Crowds were marching towards the presidential palace in Khartoum when security forces fired volleys of tear gas that formed thick and choking clouds, witnesses said. “Our marches will continue until we restore our revolution and our civilian government, even if martyrs fall among us,” said Mojataba Hussein, a 23-year-old protester.