Yemeni police shot dead four people in Aden on Thursday in clashes with protesters calling for southern independence on the first anniversary of the ouster of autocratic leader Ali Abdullah Saleh, their movement said.
The police fired on the protesters after thousands of them had gathered at a square in the southern port city, Fathi Ben Lazraq, a member of the Southern Movement, told AFP.
Three activists "were killed by police gunfire as they were trying to reach the place where the rally was being held," said Ben Lazraq, adding that a passerby was also shot dead.
A rival rally was held in the same spot by members of the Islamist Al-Islah (reform) party, in support of unity and of President Abdrabuh Mansur Hadi, whose uncontested election ended 33 years of iron-fisted rule under Saleh.
The powerful Southern Movement is demanding independence for south Yemen, and had warned of unrest if Al-Islah went ahead with rival demonstrations.
Twenty-eight southerners were also wounded by the police in clashes around Aden on Thursday, as they tried to prevent protesters from entering the city from neighbouring provinces, according to the group.
Two policemen were wounded by sniper fire from the rooftops of buildings surrounding the protest square, security officials said.
Aden was paralysed on Thursday as security forces deployed heavily around the city, and amid fears by residents that the rival rallies would degenerate into violence, an AFP correspondent reported.
Thousands of Al-Islah supporters gathered in the area, waving Yemeni flags and holding portraits of Hadi as well as banners reading "unity is our strength".
The southerners, for their part, carried flags of the former South Yemen, which was a separate state before unification with the north in 1990. They also displayed pictures of Ali Salem al-Baid, who served as the last president of the region before union.
"Revolution in the south, occupiers go out," they chanted.
South Yemen broke away in 1994, sparking a civil war, before it was overrun by northern troops.
Saleh, the former president, was formerly replaced by Hadi on February 21, 2012 after a year-long deadly uprising to oust him, under a UN-backed power transition agreement brokered by the Gulf Cooperation Council.
Some factions of the Southern Movement want autonomy for the area, but more hardline members are pressing for a return to complete independence for the south where residents complain of discrimination by the Sanaa government.
The position of southerners is a major obstacle to the launch of a national dialogue promised under the power transfer agreement.
The dialogue is intended to result in a new constitution in readiness for presidential and parliamentary elections in February 2014 that would end the two-year transition.
Several leaders of the Southern Movement have said they are ready to join the dialogue, but the hardline separatist faction of Baid has refused to take part.
The increasingly restive south has been hit not only by the Southern Movement's campaign for self-rule but also by deadly clashes between the army and militants loyal to Al-Qaeda.