Updated

Aid groups warned of the plight of civilians in Yemen's contested Hodeida where casualties are mounting a Saudi-led coalition is fighting to take the port city from the country's Shiite rebel.

Amnesty International warned late Wednesday that rebels have taken up positions on a Hodeida hospital rooftop, raising concerns they are using the hospital's patients as human shields to ward off coalition airstrikes. Doctors Without Borders, meanwhile, said it was treating two dozen wounded from the latest offensive.

The push against the Iran-backed rebels also known as Houthis who are holding Hodeida began anew this month, shortly after the United States called for a cease-fire by the end of the month.

Apparently in a rush to try to take Hodeida before then, coalition artillery, helicopter gunships and airstrikes have pounded the rebels since then, with dozens killed on both sides. The rebels admit they are outnumbered but have vowed to fight on.

Cease-fires in Yemen's civil war have rarely held, and peace talks have repeatedly broken down in the past.

Amnesty urged the warring sides to protect civilians. It said that the coalition, which relies heavily on air power, has killed scores of civilians in recent airstrikes, and rebels are responding with mortars in residential neighborhoods that cause indiscriminate casualties.

"The presence of Houthi fighters on the hospital's roof violates international humanitarian law," said Amnesty's Samah Hadid, adding that "this violation does not make the hospital and the patients and medical staff lawful targets" for the coalition.

Hadid said the hospital was full of wounded "civilians who have nowhere else to go for lifesaving medical care. Anyone attacking a hospital under these conditions risks responsibility for war crimes."

The conflict in Yemen, the Arab world's poorest country, began with the 2014 takeover of the capital, Sanaa, by the Houthis who toppled the internationally recognized government. The Saudi-led coalition has been fighting the rebels since 2015, in an attempt to restore that government to power.

In recent days, fighting intensified with troops trained by the United Arab Emirates, a coalition member, advanced in eastern Hodeida, pushing toward the city's port and key Red Sea facilities, some 5 kilometers (3 miles) away.

Doctors Without Borders reported an influx of wounded civilians in recent days, with 24 wounded, including women and children from Hodeida, with mostly blast and gunshot injuries.

The aid group, known under its French acronym MSF, said civilians were reported leaving Hodeida over the weekend but that it was difficult to assess how many remained trapped inside.

The Saudi-backed Yemeni President Abed Rabbo Mansour Hadi appointed a new defense minister to fill a role that had been empty for several years, naming Mohammed al-Maqdishi for the post, according to the state SABA news agency late Wednesday. He also appointed Abdullah al-Nakhi as the new chief of staff, the agency reported.