Ancient sculptures and other artefacts have been removed from the National Museum of Syria in the capital, authorities report.
The robbery was discovered on the start of the week, when employees reportedly found that an entrance had been forced from the inside.
The half-dozen missing statues were crafted from marble and dated back to the Roman era, a source told the news agency.
The nation's antiquities authority said it had launched a probe to establish the "events surrounding the theft of a collection of items", and that steps had been implemented to improve protection and surveillance.
The chief of internal security in Damascus province, General Osama Atkeh, was referenced by the official media as stating that security forces were examining the robbery, which he said had focused on several "historical artifacts and rare collectibles".
He added that guards at the museum and other persons were being interrogated.
The cultural institution, which was created in 1919, contains the significant historical artifacts in Syria.
It contains ancient inscribed tablets tracing back to the ancient era from historical site, where indications of the earliest complete alphabet was found; early centuries CE ancient art from the ancient city, one of the most important ancient sites of the historical period; and a ancient synagogue that was constructed at another archaeological site.
The facility was compelled to shut in the early 2010s, twelve months after the outbreak of the devastating civil war. Most of the holdings was transferred and preserved at secure places to ensure their safety.
It began limited operations in 2018 and resumed full operations in the beginning of the year, a month after insurgents removed Syria's former leader.
Each of the six of Syria's Unesco World Heritage sites were harmed or partially destroyed during the conflict.
The Islamic State group demolished numerous ancient buildings and other structures at the archaeological site, asserting that they were un-Islamic. International authorities denounced the destruction as a war crime.
Many cultural items were also lost or looted from historical locations and collections.