DONETSK, Ukraine — Despite a cease-fire declared a month ago between the Ukrainian forces and pro-Russian rebels, the biggest city in eastern Ukraine remains embroiled in fighting that includes daily artillery and rocket barrages hitting residential areas.

The fighting focusing on the airport of the rebel-held city of Donetsk shows the difficulties of enforcing a truce that has held in most other areas of eastern Ukraine since it was declared on Sept. 5.

Day after day, artillery shells and rockets fly overhead. Many explode in densely populated residential areas as the rebels have fought to dislodge Ukrainian government forces from the Donetsk airport just north of the city. Nine civilians were killed Wednesday, and a Red Cross staffer was killed Thursday. They were among scores killed and wounded since the fighting was supposed to have stopped.

“All windows in our house were shaking, I was sitting on my bed and I had to hold tight not to fall,” said Valentina Ryabchevskaya, a Donetsk resident, describing a recent shelling near her home. “Windows were shaking, doors in cabinets opened. It’s terrible how they treat people.”

The barrage has intensified this week, with shells hitting apartment buildings, a school, a bus stop, and the Red Cross office. The United Nations and the European Union voiced concern about the fighting that threatens to derail a fragile truce that has held in most other areas in eastern Ukraine since it was declared on Sept. 5.

Negotiators representing Russia, Ukraine, pro-Russian rebels and the Organization for Security and Cooperation in Europe tried to consolidate the cease-fire with a follow-up agreement to create a buffer zone that requested each party to pull its artillery 9 miles back from the frontline.

The deal has helped reduce hostilities, but fighting has continued at a few strategic locations. Donetsk, home to a million people before the conflict, has remained the main flashpoint.

The rebels have shown no inclination to pull their forces back from their biggest stronghold, and the Ukrainian forces have been equally reluctant to relinquish what they see as a key strategic asset.