CAIRO (Dispatches) -- A Saudi-led military coalition fighting in Yemen targeted its own allies with airstrikes Sunday, a day after southern separatists seized control of the strategic port city of Aden, threatening to fracture the Saudi alliance and open a new front in the five-year conflict.
Even before the damage from those strikes had been assessed, the United Nations on Sunday said that as many as 40 people have been killed and 260 injured in the previous four days of clashes in Aden that erupted on the eve of one of Islam’s holiest periods, Eid al-Adha. Tens of thousands of civilians in the Red Sea city nestled on the tip of the Arabian Peninsula have fled their homes, while many others remain trapped without basic necessities, UN officials and aid workers said.
"It is heartbreaking that during Eid al-Adha families are mourning the death of their loved ones instead of celebrating together in peace,” Lise Grande, the top UN humanitarian official Yemen, said in a statement. "Our main concern right now is to dispatch medical teams to rescue the injured. We are also very worried by reports that civilians trapped in their homes are running out of food and water.”
Yemen, the Middle East’s poorest nation, was already in the grips of what the United Nations has described as the world’s worst humanitarian crisis.
The seizure of Aden has exposed divisions within a coalition led by Saudi Arabia and the United Arab Emirates that intervened in the conflict in March 2015. Together, they have been battling to restore a former regime which resigned and then fled to Saudi Arabia in 2015.
"This weakens the coalition by exposing undeniable cracks beneath the surface,” said Elisabeth Kendall, a Yemen scholar at Oxford University’s Pembroke College. "It is becoming increasingly obvious that the UAE and Saudi Arabia do not share the same end goals in Yemen.”
Rifts have emerged over the past 18 months between the southern separatists, backed by the UAE, and forces aligned with former president Abd Rabbuh Mansour Hadi, backed by Saudi Arabia.
The separatists, who want to split Yemen’s south from its north, have long been suspicious of the former Yemeni government, ruled for decades by northerners. The separatists, and the UAE, also disapprove of Hadi’s alliance with Islah party. While the Saudis consider Islah vital for its role in Yemen, the UAE is opposed to any significant role for Islah because of its ties to the Muslim Brotherhood.
Clashes engulfed Aden’s streets after a missile attack on a military parade killed dozens of separatists fighters and a prominent commander last week.  
The violence was a major blow to Saudi Arabia and its ambition of restoring Hadi’s government. Aden had served as the government’s headquarters for several years, while Sanaa, Yemen’s capital, has been under the control of the Houthis.
Al-Qaeda and Daesh appear to be taking advantage of the security vacuum in Yemen’s south, said Kendall, who monitors both groups. In the first week of August, Al-Qaeda undertook seven operations in as many days targeting UAE-backed forces, a significant uptick in attacks. And Daesh launched two attacks in Aden, the first time it has targeted the city in more than a year.
Despite the calls for a ceasefire, the Saudi-led coalition opted to send a warning to the separatists with airstrikes late Saturday and early Sunday. The coalition did not specify where the attacks occurred, but separatist officials and aid workers said areas in the Dar Saad and Khormaksar districts, as well as around the presidential palace, were hit.
"This is only the first operation and will be followed by others .?.?. the Southern Transitional Council still has a chance to withdraw,” Saudi state TV quoted the coalition as saying, according to Reuters.
Hadi’s self-proclaimed information minister, Muammar Al Iryani, called the seizure of Aden a "coup against constitutional legitimacy”.