“A coup is ongoing here in Aden against legitimacy and the country’s unity,” Dagher said in a statement.The fierce fighting erupted on Sunday between military units loyal to President Abd-Rabbu Mansour Hadi and security forces backing southern secessionists.The separatists took control over the government headquarters in Aden, a port city that now serves as an interim capital.They were the worst clashes yet between the southern separatists – who are allied to the United Arab Emirates (UAE) – and forces loyal to the government, putting at risk their once united battle against the Iran-backed Houthi rebels in Yemen’s north.Dagher said that events in Aden were headed towards “total military confrontation” and urged members of the Saudi-led coalition, in particular the UAE, to take action.“They are moving militarily, setting up new military checkpoints and attacking camps of the [government] ….,” Ahmed bin Dagher wrote in a message on his Facebook page, referring to southern fighters under the separatist Southern Transitional Council, or STC.“This is a serious matter and the coalition and Arabs as a whole must move to save the situation. The matter is in their hands and the hope, as we see it in the government, is on the Emirates,” he said.At least 15 people were killed in the fighting, hospital sources said. Three civilians were among those killed.Medical sources told Reuters that at least 10 Yemeni fighters were killed and 30 were wounded.Ceasefire orderedHadi later ordered his forces to cease fire immediately. In a communiqué issued by Dagher to the commanders of government forces in Aden, Hadi ordered government forces “to return to base” and said all positions taken on Sunday should be vacated by all sides unconditionally.“Based on instructions from President Hadi, supreme commander of the Yemeni armed forces, and after talks with the Arab coalition … you must order all military units to cease fire immediately,” said the communiqué, which was seen by AFP.Gerald M. Feierstein, who served as the US ambassador to Yemen from 2010 to 2013, told our reporter that tensions have been simmering for a while. With so many elements working at cross-purposes on the ground, the question is now whether Yemen will remain intact or break into “two or more pieces”.“We are going to have to wait and see” whether diplomatic efforts can resolve the crisis,” said Feierstein.“Right now I am afraid that the political dialogue – the political negotiation – is frozen.”Growing crisesThe Iran-allied Shiite Houthi rebelsbegan seizing control of the Yemeni capital Sanaa in late 2014, later dissolving parliament and seizing the presidential palace. A Saudi-led military coalition launched operations in March 2015 to halt their advance.One of the Arab world’s poorest countries, Yemen now remains trapped in a proxy war between the Houthis and a US-backed military coalition headed by Saudi Arabia. The unrest has been blamed for a growing famine that the UN says will soon affect millions as well as a spiraling cholera epidemic.Mark Lowcock, the UN under secretary-general for humanitarian affairs, warned in November that Yemen faces “the largest famine the world has seen for many decades, with millions of victims” unless the Saudi-led coalition ends its blockade and allows aid deliveries into the country.In December, the International Committee of the Red Cross said the number of suspected cholera cases in Yemen had hit 1 million after the war has left more than 80 percent of the population short of food, fuel, clean water and access to health care.Years of UN-backed peace efforts have failed to resolve the conflict, which has killed more than 9,200 people.