Security forces in Yemen have shot dead at least 20 anti-government protesters in the southern city of Taiz, medics and organisers said on Monday, the BBC informs. Soldiers reportedly moved in to end a four-month-old sit-in in the city. Meanwhile, Yemen’s air force has bombed suspected al-Qaeda fighters who have seized the southern town of Zinjibar, witnesses said. President Ali Abdullah Saleh refuses to step down despite months of protests and strong opposition from a key tribe. Al-Jazeera reported that residents were fleeing the town and heading to Aden. Earlier, security officials said four soldiers were killed when their convoy was ambushed near Zinjibar.