ADEN - The United Arab Emirates carried out air strikes against government forces in South Yemen on Thursday in support of southern separatists who have deployed reinforcements to take back control of the port of Aden from their supposed allies in the Saudi-led coalition.The UAE, the second foreign power in the coalition, said it carried out air strikes against "terrorist organizations" that attacked Saudi-led coalition forces at Aden airport."The recent aggravation in offensives against the Arab Coalition forces and civilians pose a menacing threat to the security of the coalition," UAE said in a statement published by WAM news agency. "This in turn has necessitated precise and direct air strikes on the 28th and 29th August, 2019 against terrorist militias."Yemeni President Abd-Rabbu Mansour Hadi called on Saudi Arabia to intervene to stop what he called UAE interference and support for separatists battling to take over Aden.He added in a statement posted by state news agency SABA on Thursday that government forces had withdrawn from Aden to prevent the city from being destroyed, following the UAE air strikes that left dozens killed and wounded.Yemen's Defence Ministry said in a statement that more than 300 people were killed and wounded by air strikes by UAE war planes on Aden and Abyan Province.Earlier on Thursday, Southern Yemeni separatists brought in reinforcements to bolster their positions in Aden, a day after heavy fighting between the separatists and government forces with whom they were previously allied.Sporadic clashes broke out across Aden during the day and fighters from both sides patrolled deserted streets, residents said. Shops, restaurants and businesses were closed.The internationally recognized government of President Hadi, based in Aden since it was ousted from the capital Sanaa by Iran-aligned Houthi forces in 2014, said on Wednesday it had recaptured Aden airport from the separatists and controlled most of the city. Its foes disputed the claim.The outbreak of hostilities between the two sides is the latest twist in a multi-faceted war in Yemen pitting several factions and armies against each other.A Western-armed, Sunni Muslim coalition led by Saudi Arabia intervened in Yemen in March 2015 against the Houthis, and the southern separatist allied themselves with the coalition.But the United Arab Emirates has fallen out with Hadi and withdrawn many of its ground forces, prompting the separatists of the UAE-backed Southern Transitional Council (STC) to try to gain control of Aden.On Thursday, the STC said some of its troops positioned on the outskirts of the Red Sea port city of Hodeidah, which is under Houthi control, had returned to Aden to join the battle against Hadi's forces."To whoever said the Southern Resistance has fled, I say: We are here," STC vice-president Hani Ben Brik said in a social media message showing him with dozens of his fighters outside Aden's airport building.A Yemeni official said Saudi Arabia and the UAE had made contact with both sides to try to defuse the conflict, but more fighters were seen arriving in Aden and the other southern provinces of Shabwa, Lahej and Abyan.The aid charity Medecins Sans Frontieres said it had taken in 51 casualties during the fighting in Aden on Wednesday, 10 of them already dead when they reached hospital."It's total chaos here. There was fighting in the city all day yesterday. Things appear to have calmed down a bit this morning, but we expect the hostilities to resume at any point," MSF program manager Caroline Seguin said in a statement.U.N. CONCERNThe U.N. Security Council expressed concern over the increasing violence and humanitarian impact and called on all parties to show restraint and to preserve Yemen's territorial integrity. The Council also condemned increased Houthi attacks on Saudi civilian infrastructure and called for them to stop.The separatists aim ultimately to restore the South Yemen republic which merged with the north in 1990. They had clashed occasionally with government forces for several years before major new hostilities erupted this month.Saudi Arabia has called for a summit to end the standoff, which has thwarted U.N. efforts to end a war that has driven Yemen to the brink of famine and is widely seen as a proxy struggle between Iran and Saudi Arabia for regional dominance.But Hadi's government has said it will not participate until separatists cede control of sites they seized earlier in August.Hadi's forces retook Zinjibar, capital of neighboring Abyan province on Monday after securing most of the oil-producing Shabwa region and its liquefied natural gas terminal in Balhaf.