Unknown gunmen shot dead a south Yemen separatist on Sunday when they fired at a protest camp in the port city of Aden, an activist said.
The attack took place while security forces arrested two Al-Qaeda suspects, eight days after a deadly attack on the intelligence headquarters in the city.
"Gunmen fired from a car at the camp of the (Southern) Movement, killing one of the activists," Nizar al-Saadi told AFP.
He said that protesters camping in Al-Mansura neighbourhood "blocked the road" in retaliation.
Yemen's southern separatists have for decades complained of marginalisation by Sanaa. Although the movement remains fractured, it demands autonomy and in some cases independence.
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Meanwhile, two suspected Al-Qaeda militants were arrested in a raid on a house where they were hiding, said a security official.
The raid took place "near the intelligence headquarters" where 19 soldiers had been killed in an August 18 rocket attack which the authorities blamed on Al-Qaeda.
"There was an exchange of gunfire during (Sunday's) raid but no one was hurt," the official said, requesting anonymity.
Yemeni security forces have been on heightened alert since the intelligence headquarters attack. Six other suspected militants were arrested on Thursday and Friday.
Al-Qaeda loyalists have carried out a spate of deadly attacks against the Yemeni security forces and their militia allies since President Abdrabuh Mansur Hadi came to power earlier this year pledging to crush the militants.
Al-Qaeda had taken advantage of a nearly year-long uprising against Hadi's predecessor, veteran strongman Ali Abdullah Saleh, to seize large swathes of the south and east.
In an all-out offensive launched in May, the army retook a string of towns in Abyan province, which neighbours Aden to the east.