Ancient sculptures and additional items have been taken from the National Museum of Syria in Damascus, authorities report.
The burglary was found on the start of the week, when staff allegedly found that one of the museum's doors had been damaged from the inside.
The six stolen statues were crafted from marble and traced back to the ancient Roman times, an authority told the media outlet.
The nation's antiquities authority said it had initiated an inquiry to determine the "details surrounding the disappearance of a number of items", and that steps had been implemented to strengthen protection and surveillance.
The head of national security in the Damascus region, Security Chief Atkeh, was cited by the state-run Sana news agency as saying that security forces were investigating the incident, which he said had focused on several "historical artifacts and valuable objects".
He noted that museum protectors at the museum and other persons were being questioned.
The National Museum, which was created in 1919, houses the primary cultural treasures in Syria.
It includes clay cuneiform tablets originating to the 14th Century BC from Ugarit, where evidence of the earliest linguistic system was uncovered; early centuries CE Greco-Roman sculptures from historical site, one of the most important ancient sites of the classical era; and a ancient synagogue that was built at Dura Europos.
The museum was forced to close in the early 2010s, one year after the start of the devastating civil war. A large portion of the holdings was evacuated and kept at secure places to ensure their safety.
It partially resumed in recent years and completely reopened in early this year, four weeks after rebel forces overthrew Syria's former leader.
All six of nationally recognized sites were affected or significantly impacted during the civil war.
The IS organization blew up multiple ancient buildings and other structures at Palmyra, asserting that they were idolatrous. Unesco condemned the demolition as a atrocity.
Many historical objects were also lost or looted from archaeological sites and cultural institutions.
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