Tens of thousands of people rallied in Yemeni capital Sanaa on Monday to celebrate the second anniversary of the country's uprising and push for further change.
Officials said that two people were killed and dozens wounded in clashes between Islamists and southern separatists.
Security forces said one bystander and one separatist were killed as Islamist party Islah members fought independence supporters in Aden.
Demonstrators were marking the start of the year-long struggle for better economic conditions that culminated in the resignation of president Ali Abdullah Saleh.
They demanded that Mr Saleh face charges for the killing of protesters during the uprising.
Among them were Forty-five people killed on March 18 2011 when government unleashed security forces on peaceful protesters at the "Friday of Dignity" demonstration.
US-based group Human Rights Watch said the investigation should be reopened to avoid "perpetuating the culture of impunity at the heart of Yemen's uprising."
Monday's protesters also urged current President Abdu Rabbo Mansour al-Hadi to demand an end to US drone attacks in Yemen.
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