A prison guard was killed and a colleague wounded in a gun attack in the port city of Aden, police said on Saturday, as southern Yemen observed a "civil disobedience" campaign called by separatists.
The overnight attack came as several district of the main southern city, including Mansura, Sheikh Othman and Crater, were brought to a virtual standstill by the protest action.
Police said the shooting took place when a police vehicle from Mansura prison arrived at the local hospital carrying a sick inmate. The assailants fled the scene.
On Saturday morning, dozens of southern activists used rocks and logs to block main roads around Aden, where shops, banks and schools stayed closed, an AFP correspondent said.
Pro-autonomy groups have staged such actions every Wednesday and Saturday since February 21 in protest at killings of southern activists in confrontations with security forces.
On March 18, President Abdrabuh Mansur Hadi warned Yemenis against the use of force to express political views, as he opened a national dialogue to pave the way for the drafting of a new constitution and the staging of elections.
The dialogue, scheduled to run six months, brings together 565 representatives of Yemen's various political groups -- from secessionists in the south to Zaidi Shiite rebels in the north, in addition to civil society representatives.
Most southern factions finally agreed to take part after months of negotiations and under UN pressure.
But the movement's hardliners led by South Yemen's former president Ali Salem al-Baid have dug in their heels, insisting instead on negotiations between two independent states in the north and south.
After the former North and South Yemen united in 1990, the south broke away in 1994. The secession triggered a short-lived civil war that ended with the region being overrun by northern troops.