Yemen has come under heavy international pressure to end the northern war and focus on fighting al-Qaeda, whose Yemen-based wing claimed responsibility for a failed attack on a US-bound plane in December.
Yemeni police on Thursday killed a bystander and wounded three others when they opened fire on a separatist rally in the south of the country, activists said.
Several thousand protesters had gathered for a weekly demonstration in support of prisoners, chanting pro-independence slogans such as "Occupation out!" and "Long live free south Yemen".
|Yemeni protesters shout anti-government slogans in the south of the country [EPA]
Police dispersed them with gunfire and killed a vender in a marketplace and wounded three passers-by, activists from the Southern Movement said.
On Thursday last week, three activists were killed and five others were wounded in clashes in Daleh and several other southern cities.
Pro-independence demonstrations have increased in the south in recent months amid a worsening economic situation and complaints of discrimination in favour of northerners by the Sanaa government.
South Yemen was independent from 1967 until 1990, when it united with the north.
The south seceded in 1994, sparking a short-lived conflict that ended when the south was overrun by northern troops.
Many in the south - home to Yemen's oil industry - complain northerners have seized resources and discriminate against them.
Analysts have said the truce agreement between the government and Houthi rebel fighters in the north, who belong to the minority Zaidi sect of Shia Islam, was unlikely to last as it does not address the rebels' complaints of discrimination by the goverment.
Mohammed Abd al-Salam, a spokesman for the Houthi group, said "this issue, once resolved, will serve the cause of peace".
The Sanaa government on Tuesday said that the Houthis were failing to meet some of the six key points of the ceasefire agreement and accused them of "procrastination".
Abd al-Salam said the rebels have not been dragging their feet in implementing the terms of the ceasefire.