Hundreds of families are trapped in their homes by weeks of fierce fighting in the center of the southern city of Aden, running short of supplies — their only lifeline coming from volunteers making dangerous runs across the city's harbor in rickety boats bearing food and medicine.

Their plight is just one level of the misery wreaked on Aden, once Yemen's commercial hub, by a month of unrelenting urban warfare as Shiite rebels and their allies in the military try to capture the city, battling with local militiamen as warplanes from a Saudi-led coalition pound the city with airstrikes trying to stop the rebel advance.

Infrastructure in the city, once home to a million people, has been systematically destroyed, whether in ground fighting by the two sides or by airstrikes. Wheat is scarce after grain silos at the port were destroyed by airstrikes after the rebels, known as Houthis, took refuge in them — leaving city bakeries with shortages of flour. Other strikes have pounded hotels and schools — even the city's main shopping mall — used as gathering points of Houthis and their allies. Aden's main hospital was stormed by militias, snatching some people receiving treatment as doctors and patients fled, according to the U.N.

"They are starving us," said Mohammed Mater, a resident who has been trapped in his home for weeks along with his wife and seven children, with no electricity or running water. They have been surviving, he said, on canned tuna, dates and rice. As he spoke by phone to The Associated Press, his 4-year-old daughter Aisha interrupted him in the background, asking, "How long the war will take? Will snipers leave the hill?"

Mater's family is among thousands unable to leave their homes in the city's worst battleground neighborhoods, located in the city center. Downtown Aden is located on a peninsula jutting into the Arabian Sea, connected to the mainland by a narrow isthmus — largely controlled by the combined forces of the Houthis and their allies, troops loyal to ousted President Ali Abdullah Saleh.

The geography leaves them isolated in their home streets that have become war zones, with tanks firing in residential areas and snipers on rooftops as poorly armed militias try to fend off the Houthis and pro-Saleh forces. With ambulances unable to reach them because of sniper fire, dead and wounded often lie for days in the streets. Some families have buried loved ones in their backyards. Others have made their way to the Aden University medical school to bury them in an empty lot, several residents told AP.

"It's a big prison here. The war in front of us and the sea behind us," Mater said. "We became like street beggars waiting for anyone to drop us a piece of bread or water."

One of the few sources of supplies are the boat runs organized by a group of volunteers called "For You, Aden." Several times over the past week, the group has gathered food and medicine and delivered it by old boats from mainland neighborhoods of Aden, crossing some 3 miles across the harbor to the peninsula. One time, the boat broke down halfway and had to be pulled to safety by another ship, said Maha el-Sayyed, a volunteer with the group.

"The trip is dangerous because you can be shelled from any side, at any point especially that the food stuff is hard to hide," she said. "We know that this is a mission that we might not return from." The group has lists of families trapped in the center, but once they reach the area they often can't move past the docks because of the fighting, she said, so residents have to make a risky run to come get it themselves.

Aden is one of the main battlegrounds in a war that the U.N. and other aid agencies warn is pushing the impoverished nation into a humanitarian disaster.

On Thursday, the U.N. Secretary-General Ban Ki-moon said the country's health, water and telecommunications systems are "on the brink of collapse." Yemen imports 90 percent of its food supplies — not only have imports been disrupted, but distributing the food that does reach the remaining operating ports to other parts of the country has become difficult. Fuel prices have skyrocketed, causing food prices to spiral up as well.

Nationwide, Ban said, more than 1,200 people have been killed — though it was not clear from his statement how many of those are civilians. Last week, Rupert Colville, a spokesman for the U.N. High Commissioner for Human Rights, said 551 civilians have been killed and 1,185 wounded in the violence between March 26 and April 22. Some 300,000 people around the country have fled their homes.

Saudi Arabia launched its air campaign on March 26 in a bid to restore the government of the internationally recognized president, Abed Rabbo Mansour Hadi, who fled Yemen in the face of the advance by the Houthis. The rebels took over the capital, Sanaa, and much of the north last year and are advancing on the south. Before fleeing, Hadi declared Aden the country's temporary capital, and the city is one of the last remaining bastions of his supporters.

In Aden, tens of thousands who have fled their homes are crowded in the few relatively safe districts. Even there, food supplies are tight.

"Now the only source of food is from storage houses and these are running out," said Naguib Babli, an official at the Aden Chamber of Commerce. Water is distributed by donkey carts after water stations were either bombed or ran out of fuel to pump it to houses.

A Houthi media official, Hamed Bakhit, denied accusations that the rebels are shelling residential areas, blaming Islamic extremists. "It's not in the interest of the Houthis to target civilians," he said.

This week, pro-Saleh troops overran the neighborhood of Khor Maksar, located on the isthmus, after overwhelming militias defending the area. The troops had lists of wanted militia leaders and Hadi supporters and went house to house in the district searching for them, shooting some in the street, an Aden security official told the AP, speaking on condition of anonymity for fear for his safety.

Yasmin el-Akhali, a 39-year-old resident of Khor Maksar, said her younger brother was killed earlier in the week when he was shot in his leg and bled to death. She fled the district on Wednesday as Saleh's forces stormed in and shells hit her house, where more than 30 people were crammed in.

"It was like thunder and lightning when street battles raged around us," she said.

Abdel-Rahman Abdel-Khaleq, a well-known writer in Aden, fled his house in Khor Maksar on Friday.

"I am not afraid of the war as much as I am afraid of what will happen next," he told AP. "What kind of country I will be living in when the dust settles. Aden's infrastructure has been eliminated. There are no more airports in Aden, no hotels, no hospitals, nothing."

"The worst is yet to come," he said.

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Michael reported from Cairo.