AMMAN, Jordan - The conflict in Yemen has overwhelmed aid groups with "massive" humanitarian needs arising from months of violence and destruction, and hospitals at times had to turn away patients, the international group Doctors Without Borders said Monday.

The warning came as Yemen's pro-government forces, backed by a Saudi-led coalition, retook another district in southern Abyan province after a battle with Shiite rebels that killed dozens on both sides.

Doctors Without Borders, also known has Medecins Sans Frontieres or MSF, told reporters in Jordan that it has treated more than 10,000 war-wounded in Yemen since March, including close to 5,000 who underwent surgery.

Thierry Goffeau, MSF project co-ordinator in the southern port city of Aden, said a team of MSF surgeons have been treating dozens of shelling and sniper fire victims every day at the local Sadaka Hospital. On one day in July, more than 200 war-wounded arrived after a neighbourhood of Aden was shelled heavily, he said.

Three other local hospitals, where most foreign staff had left months ago, were at times so overwhelmed that "they had to close their doors" to patients, he said.

Fuel, electricity and water were in short supply, but one of the biggest challenges was dealing with patients' families or armed fighters escorting them, said Goffeau. He said that at times fights broke out in the triage area.

The hospital was some 500 metres from the frontline, he said. Windows were covered by metal plates to protect against stray bullets, and shells landed in the vicinity of the hospital.

Goffeau said he's worked in many hotspots over the past decade, but that the situation in Yemen was "by far" the most difficult.

Gazali Babiker, the head of the MSF mission in Yemen, said that the humanitarian situation is worrying. "The needs are massive and way beyond the capacity of aid organizations currently on the ground," he said, adding that the international community's response to the crisis has fallen short.

The Yemen conflict escalated in March when a Saudi-led, American-supported coalition began launching airstrikes against Shiite Houthi rebels and their allies - troops loyal to former President Ali Abdullah Saleh - who control the capital, Sanaa, and much of northern Yemen. They are pitted against southern separatists, local and tribal militias, Sunni Islamic militants and loyalists of exiled President Abed Rabbo Mansour Hadi.

On Monday, pro-government forces took control of another district in southern Abyan province after a fierce battle with Shiite rebels, driving out the final pocket of resistance in the province, security and military officials said. More than 35 rebels were killed as well as 15 people from the pro-government side in the battle for Lawder district, said the officials, speaking on condition of anonymity under regulations.

Yemen's deputy parliament speaker, Maj. Gen. Mohammed Shadadi, was seriously wounded and four of his bodyguards were killed in an ambush nearby and was evacuated to Aden, the officials also said, adding that he will likely be taken to Saudi Arabia for treatment.

Yemen's president, Hadi, is in Saudi Arabia, in self-imposed exile after he and most of the government fled the rebel advance earlier this year.

Pro-government fighters have had a series of victories in recent weeks after capturing Aden last month. On Sunday, they retook of Zinjibar, Abyan's capital, after three days of intense fighting, and they now say they control the entire province.

In central Taiz province, security officials said the rebels launched an offensive with heavy weaponry to retake areas they lost last week, in fighting that left 30 Houthis dead and 18 of the pro-government fighters. In Ibb province, security officials said pro-government forces made advances that could cut off rebel supplies to Taiz and the city of Dhale.

The goal of the coalition-backed forces is to drive the rebels out of Bayda and Marib provinces before heading to their northern stronghold of Sadaa, military officials said. The Saudi-led coalition launched over 100 airstrikes to support the advances on Monday, including many around the city of Mukerias in Abyan, where forces are poised to drive out the rebels, they added.