When Islamic State fighters routed Syrian government forces and took control of the ruins of Palmyra Thursday morning, the ancient city became the latest archaeological site to fall into the hands of the militant group.

The extremist group views ancient ruins as idolatrous and has looted or destroyed several heritage sites under its control in Iraq, raising fears about the fate of Palmyra - one of the best-known historical sites in the Middle East.

The UNESCO world heritage site is famous for its 2,000-year-old towering Roman-era colonnades, other ruins and priceless artifacts. Before Syria's conflict began in 2011, thousands of tourists a year visited the remote desert outpost, a cherished landmark referred to by Syrians as the "Bride of the Desert."

Syrian authorities say they moved hundreds of priceless artifacts to Damascus ahead of the IS takeover, but the fate of those ruins too large to move remains uncertain. Islamic State militants have already looted and vandalized a museum in the Iraqi city of Mosul and have massively damaged the ancient cities of Hatra and Ninevah - both UNESCO world heritage sites.

The attacks on the ancient sites are partially motivated by the group's hostility to non-Islamic and pre-Islamic cultures. But some antiquities authorities have charged that the destruction is a cover for the selling of looted artifacts on the black market. The proceeds have helped fund the group's rampage across northern and eastern Syria and northern and western Iraq, where it has carved out a self-styled caliphate governed by a violent interpretation of Islamic law.

Here is a series of images of ancient heritage sites currently under Islamic State group control.

Palmyra, northeast of Damascus, Syria:

Palmyra, northeast of Damascus, Syria

Vandals in the Ninevah Museum in Mosul, Iraq:

Vandals in the Ninevah Museum in Mosul, Iraq

Destroyed Mosque of The Prophet Jirjis in Mosul:

Destroyed Mosque of The Prophet Jirjis in Mosul

Militants destroy Iraq's Hatra archaeological site:

Militants destroy Iraq's Hatra archaeological site