Yemeni President Abdrabuh Mansur Hadi was paying a surprise visit to Aden on Sunday as witnesses said clashes raged between police and protesting southern separatists amid calls for civil disobedience.
Hadi was in Aden on an "inspection visit", his first since becoming president in February 2012, and would meet local officials and military leaders, the state news agency Saba reported.
A security official in the main southern city told AFP that Hadi was visiting to "closely check the situation in Aden following the unrest".
Protests have intensified in south Yemen since the killing of five people in clashes between police and pro-independence demonstrators on Thursday, when the deeply divided country marked a year since the ouster of strongman Ali Abdullah Saleh.
Witnesses said hardliners from the Southern Movement clashed on Sunday with security forces in the southeastern city of Mukalla after they blocked roads with burning tyres and rocks.
"The army is using live ammunition against protesters," said Nasser Baqazquz, an activist from the separatist group.
One policeman was wounded in the confrontation, according to witnesses.
In Aden itself, three protesters were wounded when army troops opened fire to open a main road in the Mualla neighbourhood, witnesses and medical sources said.
Protesters had also blocked roads in the neighbourhoods of Mansura, Sheikh Osman and Dar Saad.
Three other protesters were wounded in the city of Huta, in Lahj province, when security forces advanced to clear a blocked road, witnesses and medics said.
On Saturday, two protesters and a policeman were killed in clashes that erupted in the south, including in Aden, security officials and medics said.
In the city of Sayun in the eastern province of Hadramawt, protesters trying to enforce a programme of civil disobedience set a merchant from northern Yemen on fire, leaving him in a critical condition, witnesses said. The man is in intensive care, a medical source told AFP.
The protesters also on Saturday attacked shops in Mukalla owned by northerners, and burnt down two offices belonging to the Islamist Al-Islah (Reform) Party, which backs Hadi, witnesses said.
The party issued a statement protesting the attacks on its southern offices and urged its members to "exercise restraint".
South Yemen broke away in 1994, sparking a civil war, before it was overrun by northern troops.
The Southern Movement has been divided over participating in Yemen's national dialogue.
All its wings had agreed to join the UN-backed talks except for a faction led by exiled leader Salem Baid which insists on full independence for the south, whose residents complain of discrimination by the Sanaa government.
The conference, originally set for mid-November, has been repeatedly delayed, mainly due to differences with the southerners. It is now set for March 18.