The latest heavy fighting in a key southern Yemeni city has killed 58 civilians and wounded at least 50, medical officials said Friday, reporting the casualties from the previous day.

According to the officials, rebel shelling in the city of Taiz first killed 23 civilians, which provoked airstrikes by the Saudi-led coalition that has been targeting the Shiite rebels, also known as Houthis, since March.

The subsequent airstrikes killed 35 people and demolished five houses in the eastern neighborhood of Sala, from where the rebels launched their attacks. Of those killed, at least 10 were children, they added, speaking on condition of anonymity because they were not authorized to talk to reporters.

"It was a hellish night," said Taiz resident Omar Karim, who could not sleep from the sound of the shelling as he and his family cowered in their basement for shelter.

Yemen's fighting, which escalated in March, pits the Houthis and troops loyal to former President Ali Abdullah Saleh against southern separatists, local and tribal militias, Sunni Islamic militants and troops loyal to President Abed Rabbo Mansour Hadi, which are backed by a Saudi-led coalition.

The U.N. says health facilities in Yemen have reported more than 4,000 conflict-related deaths since March.

Meanwhile, in the port city of Aden, witnesses on the Gold Mohur beach said a masked group of armed men led six men in orange jumpsuits with their hands tied behind their backs onto a boat on Wednesday. The booby-trapped boat, they said, was dragged out to sea by another boat, before it was detonated remotely.

The explosion killed the six captives, whose identities were not known, said the witnesses, speaking on condition of anonymity fearing for their own safety.

No group claimed responsibility for the killings but Islamic State-affiliated militants have carried out such slayings in the past.

Also Wednesday, Islamic State-affiliated militants claimed an attack that killed a Yemeni soldier at a checkpoint in Hadramawt province. The Associated Press could not independently verify the claim, which was posted by IS sympathizers on Twitter Thursday.