The Yemeni police troops shot dead three southern activists during a pro-secession protest on Friday in the port city of Aden, witnesses and activists said.

The clashes broke out when the police troops opened fire in an attempt to disperse thousands of protesters who were demanding the secession of the formerly independent south, one witness told Xinhua on condition of anonymity.

"Police soldiers prevented the protesters from marching towards their protest camp in the Mansoura district in Aden," the witness said.

"About eight people were injured and three activists were killed in Friday's firefights," he added.

Activists from the pro-secession Southern Movement said that " the security forces used excessive force against our protesters. All the Mansoura's neighborhoods are under relentless blockade."

"Our struggle for southern independence will continue," the activists said anonymously.

The port city of Aden is a main stronghold of young activists demanding independence for the south.

North and South Yemen unified peacefully in 1990, but the relationship deteriorated in 1994. Calls for separation in the country's southern regions were renewed in 2007.