In the face of charges it targeted Yemeni 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.

The UAE's foreign ministry issued a statement late Thursday, hours after the separatists regained control of Aden, forcing government troops who had entered the southern port city a day earlier to withdraw.

Air strikes on Wednesday and Thursday that reportedly left dozens dead 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 main fronts -- a battle for control of Aden and the south, and the Saudi-led coalition's campaign against the Huthis in the north.

In further violence in the port city on Friday, the Islamic State group claimed a suicide bombing that killed three separatist fighters, while a separatist military chief survived a roadside bomb that wounded five of his guards, security sources said.

The suicide attack wounded and killed "members of the Security Belt... in an explosion of a motorbike-borne device in the Saad area of Aden," IS said via its propaganda arm Amaq, referring to the UAE-backed force of southern separatists who control the city.

Security sources had initially blamed both attacks on Al-Qeada, and said separatist forces made several arrests, adding that they aimed to dismantle jihadist "sleeper cells".

But residents have reported arrests of soldiers loyal to the internationally recognised government.

On August 1, separate attacks in Aden by jihadists and Huthi rebels killed 49 people, mostly separatist fighters.

The separatist Southern Transitional Council (STC) accused the government of complicity in the attacks, sparking a showdown between the two sides.

The intensifying conflict between Abu Dhabi and the government undermines the coalition, and poses a headache for regional powerhouse Saudi Arabia, which is focused on fighting 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 Yemen's 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 STC, Aidarus al-Zubaidi, who aims to regain independence for South Yemen, which was forcibly unified with the north in 1990.

At a press conference in Aden on Thursday, he said that among fighters captured during the 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 exile 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.

Yemen's 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 interim 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 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".