SANAA, Yemen (AP) — Shiite rebels and their allies randomly shelled an area north of Aden on Sunday, killing at least 45 people and wounding over 100, officials said.

The rebels are pushing back against an offensive by their Saudi-backed rivals that uprooted them from areas they control in the strategic port city last week, including the Aden international airport.

The officials said hundreds of residents fled Dar Saad, north of Aden, amid shelling that intensified Sunday from the rebels. They said at least 45 people, believed to be civilians, were killed. Ambulances rushed to various areas in the town, taking the wounded to various hospitals, including some operated by the international aid group Doctors Without Borders.

The officials spoke on condition of anonymity as they weren't authorized to brief journalists.

Abdu Mohammed Madrabi, a 65-year old resident of the town, said he was in line outside the post office to collection his pension when the shells hit, causing chaos in the area. Madrabi, who was wounded in the neck, back and leg, said many private cars carried the wounded to hospitals because ambulances couldn't cope.

"We are now sitting on the floor of the hospital" waiting for treatment, he said.

The shelling was intense in the neighborhood of Sharqiya, hundreds of meters (yards) from the post office. Residents said shelling since early dawn kept them hiding at home.

"It's been one shell after the other since the morning. We are feeling the house is going to collapse over our head," said Arwa Mohammed, a resident of Sharqiya, who has been locked up in one room with her seven-member family for safety. She said a shack nearby was burning from the bombing, adding that its residents fled only minutes before the shell landed.

"Balls of fire are falling over our heads amid screams of children and women," said Anis Othman, a neighbor of Mohammed. "Why all that shelling? There are no weapons or fighters here. They (rebels) want to terrorize us and drive us out. This is only rancor and hate."

Hassan Boucenine, the head of Doctors Without Borders in Yemen, said the situation is "very, very difficult," describing random shelling in Dar Saad that is coming from the north and east, wounding mostly civilians. He said his medical facilities have received 50 wounded people and 25 corpses.

"There will be more," he said.

The Saudi-backed fighters, backed by Saudi-led coalition airstrikes, pushed the rebels out of Aden's airport and two major neighborhoods last week. The rebels vowed to retaliate.

Aden has been the scene of some of the war's most intense ground fighting since March.

Associated Press writer Sarah El Deeb in Cairo contributed to this report.