Yemeni security forces shot and killed one activist and wounded at least four other people on Saturday during clashes with southern separatists who had blocked roads and attacked police, medics and witnesses said.
U.S.-allied Yemen, thrown into political disarray in early 2011 when mass protests ousted long-time ruler Ali Abdullah Saleh, still faces frequent fighting between separatists and security forces.
Witnesses said Saturday's clashes erupted in the southern port of Aden when protesters demanded the release of activists detained during fighting that killed six people on February 21, the first anniversary of President Abd-Rabbu Mansour Hadi's election.
They said the protesters, who had blocked roads and forced shops to close down, were also demanding security forces responsible for opening fire on demonstrators be put on trial.
Security forces who arrived at Saturday's protest in the city's al-Mansoura district, opened fire at stone-throwing youths and armed men in the crowd, witnesses said.
A 23-year-old youth was killed and four other people were injured by live rounds, said medics. The casualties were taken to a private hospital for treatment to avoid being subjected to questioning by security forces.
A Yemeni security official confirmed some people had been injured by shots fired by security forces who were responding to attacks on them while they tried to reopen blocked roads.
He said he was not aware of any deaths.
North and South Yemen merged into one country in 1990 when the collapse of the Soviet Union undermined the communist south's economy. But political harmony in the Arab world's poorest country was short-lived and an attempted southern secession in 1994 prompted civil war, won by the north.
Southern Yemenis, complaining of discrimination by the north, favor creating another independent socialist state.