Five civilians among 20 people reported dead as fighting between separatists and government forces go on for third day.
Thousands of people have marched in Aden to express their support for separatist fighters who seized the southern port city from forces loyal to Yemen’s internationally-recognised government.
The demonstrators on Thursday rallied in the Khormaksar district, waving southern flags and banners proclaiming loyalty to the separatist Southern Transitional Council (STC).
Protesters chanted “Oh Revolution of the South” and waved flags of the old state of South Yemen. Yemen was split into two countries during much of the Cold War before unifying in 1990.
The protesters demanded the separatists from the STC hold on to positions in Aden that they had taken in last week’s fighting, in which at least 40 people were killed and 260 wounded, according to the United Nations.
Organisers said many of the demonstrators had travelled into the city from neighbouring southern provinces to add their voice to the calls for secession.
Separatist forces trained and equipped by the United Arab Emirates (UAE) seized the presidential palace in Aden on Saturday following days of clashes with fighters loyal to the government of President Abd-Rabbu Mansour Hadi.
On Wednesday, Deputy Foreign Minister Mohammed Abdullah al-Hadrami called for the STC to withdraw from areas they seized and to hand over arms to the government of exiled Hadi.
Saudi Arabia, which along with the UAE has led a ferocious military intervention supporting the government against Houthi rebels from the north, has also called on the separatists to pull back to clear the way for dialogue.
However, a petition signed by southern civil society organisations and trade unions called on the Saudi-led coalition to hand over administration of the south to the separatist STC.
It urged STC chief Aidarus al-Zubaidi to declare independence and appealed for international recognition for the breakaway state.
The escalation in Aden has now made Yemen’s civil war even more complex as combatants in the southern port city are nominal allies in the Saudi-led coalition, which has been battling the Houthis in northern and western Yemen since March 2015.
The UAE, which recently announced the beginning of a troop withdrawal from Yemen, has armed and trained an estimated 90,000 allied fighters in the south.
Yemen’s long-running war has triggered what the UN describes as the world’s worst humanitarian crisis, with 24.1 million – more than two-thirds of the population – in need of aid. Tens of thousands of people have been killed and millions forced from their homes.