The Syrian army and its allies advanced Tuesday east of Palmyra after retaking the ancient city from forces loyal to the Islamic State group, also known as ISIS, earlier this month and making gruesome discoveries left behind by the jihadists' retreat.

Syria's so-called "pearl of the desert," home to some of the world's most well-preserved Roman Empire ruins, was found to be littered with the mutilated corpses of ISIS militants and their victims, according to RT.

Some of the dead appeared to be casualties of this month's combat as the Syrian army, backed by Russia, Iran and allied militias, dislodged ISIS forces from the city's historic sites — some of which ISIS intentionally demolished. Other bodies showed signs of execution, including beheading, at the hands of the ultraconservative Sunni Muslim group.

Read: Syrian Army, Russia Battle ISIS For Palmyra

A media team reportedly found the bodies of children recruited by ISIS and sent to the battlefront. Moscow-based press also said it discovered at least four Syrian army soldiers, which local military sources said would ultimately be recovered and returned to their families as soon as the government's limited resources would allow.

The Syrian government, led by President Bashar Assad, has been at war with various armed rebel groups after mass opposition protests in 2011 transformed into an insurgency against the state. ISIS took advantage of the chaos, expanding into Syria from neighboring Iraq and fighting alongside the opposition until clashing with other anti-government groups. ISIS managed to take control of a large portion of Syrian territory but has since been beaten back by various groups and their international sponsors, including the Russia-backed Syrian army, Turkey-backed Syrian rebels and the U.S.-backed Syrian Democratic Forces (SDF), which are comprised of a Kurdish majority and representative of a number of the country's ethnic communities.

Read: US, Russia Team Up Against Turkey To Protect Kurds

The three nations and the forces they endorse have nearly converged in northern Syria, driving ISIS militants back to their de facto capital of Raqqa, where Russia, Turkey and the U.S. have all planned to stage a final assault to eradicate the group.

However, violent rivalries between the advancing forces have emerged as they all contend to increase their influence over Syria and the outcome of its six-year civil war that has killed hundreds of thousands and displaced millions more.