Tens of thousands of people rallied in south Yemen's key city Aden Sunday demanding renewed independence, as Shiite militiamen sought to expand their control over more of the impoverished country.

The southerners were marking the 47th anniversary of the end of British colonial rule in 1967, which created an independent state that lasted until union with the north in 1990.

Sunday's protest was called by the Southern Movement which is campaigning for autonomy or outright secession for the previously sovereign south.

Waving the flag of what used to be South Yemen, protesters who poured into Aden from neighbouring southern provinces vowed not to let up until they achieve independence.

"We will not back down until we achieve victory -- liberation and independence," read banners at a square in Aden, where secessionists have been camped out since October 14.

The rally reflects the "rejection of the people of the south of all projects and initiatives that do not fulfil their legitimate right to freedom, sovereignty, and independence", a hardline Southern Movement leader, Hassan Baum, told supporters at the rally.

Renewed independence for South Yemen will "ensure security and stability" in the Arabian Peninsula country, said the head of the supreme council of the Southern Movement, a faction within the movement.

Yemen continues to reel under the impact of expansion by Shiite militiamen who overran the capital in September and seized a major port unopposed, before clashing with Sunni tribes and Al-Qaeda south of Sanaa.

The southern separatists, as well as the Shiites from the north, rejected plans unveiled in February for Yemen to become a six-region federation, including two in the south.