UNESCO via AP, File, Ron Van Oers
FILE - This undated file image released by UNESCO shows the site of the ancient city of Palmyra in Syria. A satellite image on Aug. 31, 2015 shows that the main building of the ancient Temple of Bel in Palmyra has been destroyed, a United Nations agency said. Experts, conservators and local residents are scrambling to document Syria's millennia-long cultural heritage that has been damaged by the country's war since 2011, by battles against the Islamic State group and by its intentional destruction.

BEIRUT — Syrian government planes carried out several airstrikes and dropped barrel bombs on the IS-controlled city of Palmyra for the third straight day on Thursday, forcing hundreds of civilians to flee their homes in the ancient city, activists said.

The bombardment, which included at least six barrel bombs on Thursday alone, did not ease up even as Muslims began marking the Eid Al-Adha holiday, said a Palmyra resident.

Most of the city's few remaining residents have hunkered down in shelters, while hundreds fled early in the morning in rented buses to Raqqa, another IS-controlled city about 270 kilometers (170 miles) from Palmyra, said the resident. He spoke to The Associated Press on condition of anonymity, fearing for his life.

Medical supplies in Palmyra were dwindling, and there have been deaths from lack of medical treatment or medicines, he added. Death tolls were hard to estimate and only one small hospital was operational. Many are quickly buried, without funeral ceremonies.

The Britain-based Syrian Observatory for Human Rights, which relies on a network of activists on the ground, also reported airstrikes on Palmyra for the past three days. The group confirmed the shortage of medical supplies, which is contributing to the increasing death toll.

Palmyra was overran by IS militants in May and the group has since used the ancient city, strategically located in Syria's central Homs province, to launch attacks on neighboring areas, including an oil and gas fields. The IS has also destroyed some of Palmyra's ancient sites, posting dramatic images of 1st century temples being blown up. The Islamic State considers such relics as promoting idolatry.

The government's renewed bombing campaign appears to be part of its new policy to focus on IS-controlled areas, said the head of the Observatory, Rami Abdurrahman. Russia has been lobbying the U.S.-led international coalition against the Islamic State to coordinate with the Syrian government on airstrikes against the militants.

The Palmyra resident, who spoke to the AP through social media, said each person paid about $3.5 for the bus ride to Raqqa. Thousands have already fled the city after IS captured it in May.

Other activists posted pictures of Palmyra residents arriving in Raqqa.

Nearly half of Syria's pre-war population of 23 million is either displaced in the country or has fled to neighboring countries or recently rushed to Europe for sanctuary.