The protest was the second since May 4 when thousands of southerners marched in support of former Aden governor Aidarous al-Zoubeidi after he was sacked by President Abedrabbo Mansour Hadi.
After being fired in April, Zoubeidi set up the South Transition Council, an autonomous body whose 26 members include the governors of five southern provinces and two government ministers.
The body chaired by Zoubeidi aims to "run the southern provinces" and "represent them inside and outside" the country.
The port city of Aden is Hadi's home town and where his government, which is battling Shiite Huthi rebels who have seized the capital Sanaa, is based.
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Today's protesters, who flooded Aden from several southern provinces, defended Zoubeidi's council, chanting "Independence is our objective" as they marched.
The South Transition Council released a statement pledging to "pursue the mission of liberating" south Yemen -- which was an independent state until 1990 when it was unified with North Yemen.
The two men played key roles in restoring security to Aden and adjacent provinces after rebels were pushed out in 2015.
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