Already ravaged by five years of civil war, Yemen is sinking further into chaos. Separatist fighters announced on Saturday (August 10th) that they have taken control of the presidential palace in Aden after four days of fighting in the southern city, the "temporary" capital of President Abd Rabbo Mansour Hadi's government in exile in Riyadh (Saudi Arabia).

If the catch is mostly symbolic - the president is absent - it is nonetheless a turning point in the clashes that have shaken Aden since Wednesday.

"We took the palace to the forces of the presidential guard without a fight," assured AFP a spokesman for a separatist military force called "cordon de sécurité".

The Yemeni government has accused the UAE of being "responsible for the coup" of the separatists in Aden.

According to military and security sources, separatist fighters had earlier in the day seized three barracks of government forces in Aden, where loyalist power has established its headquarters, since the country's historic capital, Sanaa, in north, is in the hands of Houthi rebels.

At least 18 dead in the fighting

Since Wednesday, separatist fighters and government soldiers have clashed, all of whom have, in theory, been allies since 2015 in a coalition led by Saudi power in Ryad and the Emirati government of Abu Dhabi.

This motley Arab-Sunni coalition fights in the north of the country against Iranian-backed Shiite Houthi rebels.

The fighting in Aden between separatist elements of the "Cordon de sécurité", supported by the United Arab Emirates, and government troops, have killed at least 18 people (combatants and civilians), according to doctors and sources of security. According to the organization Doctors Without Borders (MSF), more than 75 injured people have been treated in a hospital under this NGO since Friday.

Prevent any military escalation

Even before the presidential palace fell, Deputy Foreign Minister Mohammed al-Hadhrami of the Hadi government had sentenced via Twitter a "coup against legitimate institutions" in Yemen.

Emirati Foreign Minister Abdullah bin Zayed said he was "very worried" and said "to make every effort to calm the situation and de-escalate".

He called on UN Special Envoy Yemen Martin Griffiths to do the same, according to a statement to the official UAE WAM news agency.

"The important thing is to intensify the efforts of all parties on the main front", the one against the Houthis, he added.

The Yemeni government on Thursday urged Saudi Arabia and the UAE to "urgently pressure" those supporters of an independent southern Yemen "to prevent" any military escalation.

North-South hostility

The clashes in Aden further complicate the situation in Yemen, where tens of thousands of people, including many civilians, have already died as a result of the civil war, according to various humanitarian organizations.

About 3.3 million people are still displaced and 24.1 million (more than two-thirds of the population) need assistance, according to the UN.

South Yemen was an independent state until 1990. In the south, resentment is strong against Yemenis from the North, accused of forcing the unification of the country by force.

To this North-South hostility is added the conflict within the heterogeneous coalition initially formed to defend the government.

This is not the first time that the separatists of the Southern Transitional Council (TCC) - which includes the "Cordon of Security" forces - oppose units loyal to President Hadi.

Fighting between separatists and forces loyal to the president had already killed at least 38 people in January. The situation had calmed down only after a concerted intervention between Saudi Arabia and the United Arab Emirates.

Yemen is now facing the risk of a "civil war in the civil war" already ravaging the country, according to a report by the International Crisis Group (ICG).

With AFP