In the face of charges it targeted government troops, Abu Dhabi said it acted in self-defence against "terrorist militias" threatening the Saudi-led military coalition against Huthi rebels in which the UAE is a key partner.

A foreign ministry statement was issued late Thursday shortly after the separatists regained control of Aden, forcing government troops who had entered the southern port city a day early to withdraw.

Air strikes on Wednesday and Thursday hit "armed groups affiliated with terrorist organisations", Abu Dhabi said, in a reference to Islamists it believes make up part of Yemeni government forces.

The operation "was based on confirmed field intelligence that the militias prepared to target the coalition forces -- a development which required a preemptive operation to avert any military threat", it added.

The accusations risk straining an already complex conflict in Yemen, which is being fought on two fronts -- a battle for control of Aden and the south, and the Saudi-led coalition's campaign against the Huthis in the north.

The conflict between Abu Dhabi and the government undermines the coalition, and poses a headache for regional power Saudi Arabia which must focus energies on the fight against the Huthis who are aligned with Riyadh's arch foe Iran.

The air strikes came in a see-sawing battle between the government and southern separatists who have tussled for control of Aden and the neighbouring provinces Abyan and Shabwa over the past three weeks.

- Saudis as peacemakers? -

Yemen's government on Thursday accused the UAE of mounting the air strikes in support of the separatists, in an assault it said killed 40 combatants and wounded 70 civilians.

The UAE, which has a zero tolerance policy towards Islamists, believes that part of the Yemen army is made up of militants from Al-Islah, a party considered close to the Islamic Brotherhood.

The allegation was backed by its Yemeni ally, the head of the Southern Transitional Council (STC), Aidarus al-Zubaidi, who aims to regain the independence of South Yemen which unified with the north in 1990.

At a press conference in Aden on Thursday, he said that among fighters captured during their retaking of the city were "internationally wanted terrorists".

However, Yemeni President Abedrabbo Mansour Hadi redoubled his allegations against the UAE, accusing it late Thursday of having planned, financed and coordinated attacks on state institutions and military positions in Aden.

The Yemeni head of state, who is in exiled in the Saudi capital, called on Riyadh to "intervene to halt the blatant interference of the United Arab Emirates, in support of the militias, and air raids against the armed forces of Yemen ".

The UAE's minister of state for foreign affairs, Anwar Gargash, on Friday urged all sides to go back to the negotiating table under a Saudi proposal for talks in Jeddah.

The Yemen government has said the STC must first withdraw from its positions.

"The Saudi initiative is the way out of this crisis," Gargash said on Twitter.

The coalition intervened in Yemen's war in 2015 in support of the government after the Huthis swept south from their northern stronghold to seize the capital Sanaa and much of Yemen -- the Arab world's poorest nation.

The strategic port city of Aden has since then served as the government's capital.

Fighting over the past four years has already claimed tens of thousands of lives and sparked what the United Nations calls the world's worst humanitarian crisis.

"The situation is very fragile. Families are again trapped in their homes by fighting, unable to secure food and reach medical care," the UN humanitarian coordinator in Yemen, Lise Grande, said of the recent battle for the south.

The UN Security Council on Thursday voiced concern over the clashes, including what it called a "violent attempt to take over state institutions".

It urged all parties to "show restraint and to preserve Yemen's territorial integrity".