BEIRUT: ISIS attacked the Syrian army near the city of Palmyra Thursday, killing dozens of soldiers and advancing to within 4 kilometers (2.5 miles) of the city, an activist group said.

The Syrian army, backed by Russian jets, recaptured Palmyra, the site of a Roman-era city and spectacular ruins, from ISIS in March after the jihadist group seized it in May 2015.

On Thursday the jihadists gained control over Qasr al-Halabat, to the southwest of Palmyra, Jabal Hayan, to the west, South Sawamea to the northeast and the Hawaisis region to the northwest, the Syrian Observatory for Human Rights said.

At least 34 Syrian soldiers were killed, including at least eight officers, and there were also deaths on ISIS's side, the Observatory said.

ISIS has been on the back foot in both Syria and Iraq since late last year, losing much of its territory in both countries as well as some of its most senior figures, killed in airstrikes.

The group took advantage of chaos during Syria's civil war to seize territory there and in Iraq in the summer of 2014.

Syria's civil war pits President Bashar Assad, backed by Iran, Russia and Shiite militias against mostly Sunni rebels.