Four civilians were wounded as police clashed with demonstrators in several neighbourhoods of the port city, which served as the southern capital before unification with the north in 1990.

Police have been out in force in and around the city since Monday to snuff out any demonstrations, witnesses said.

The situation was tense in other southern towns, including Lahij, Abyan and Dhaleh.

Three policemen were wounded in Dhaleh when thousands of protesters took to the streets chanting anti-government slogans and calling for the south to break away, witnesses said.

There have been sporadic clashes between police and protesters in the south over the past few months. At least 18 people have been killed, five of them policemen, since the protests erupted in late April.

The government has blamed the unrest on southern rebels demanding secession, but many in the impoverished south have been protesting against bad living conditions.

Socialists who formerly ruled the south led a secession bid in 1994 that sparked a two-month

 civil war before the uprising was crushed by northern forces loyal to President Ali Abdullah Saleh.

AFp