Thousands of Yemenis rallied in the port city of Mukalla on Sunday to demand statehood for the formerly independent south 20 years after the crushing of a secession bid.

The rally was organised by the hardline wing of the Southern Movement which is clamouring for the renewed independence of the south, 20 years after a civil war ended with its occupation by northern troops.

The separatists rejected plans unveiled in February for six-unit federation in which two regions are planned for the south, one based in Mukalla and the other in the largest southern city, Aden, where a pro-independence rally also took place on Sunday.

The south was independent between the end of British colonial rule in 1967 and its union with the north in 1990.

A secession attempt four years later sparked a brief but bloody civil war that ended with northern forces occupying the region.

"This rally is a message addressed to the world saying that the south is under occupation," said activist Basser Bakazkuz.

In Aden, police prevented protesters from reaching a main square in the city's diplomatic district, witnesses said.