ISIS says it has destroyed two shrines near the ancient city of Palmyra, which the group seized a month ago.
Photographs posted online appear to show the shrines, 4 kilometres away from Palmyra, destroyed.
This is the first report of destruction in the ancient site of Palmyra, and follows international concerns about the fate of the ancient ruins in the city.
Palmyra is a 2,000-year-old antique city home to Roman era ruins, which was added to the UNESCO World Cultural Heritage List in 1980.
Photographs show smoke rising out of the shrine of Mohammed Bin Ali, a companion of the Prophet Muhammad's cousin, Ali.
Another shrine that was destroyed belonged to Nizar Abu Bahaa Eddine, a Sufi scholar, who was buried 500 years ago.
ISIS earlier vowed to destroy the statues and shrines as the group considers them examples of idolatry.
A few days ago ISIS reportedly laid explosives under the ruins of the city as Syrian regime forces are step up efforts to recapture the city.
ISIS seized the ancient city of Palmyra in May as Syrian regime troops withdrew from the region after fierce fighting with the militants.
Palmyra has a significant and strategic location in the middle of Syria as it links the capital Damascus with the northeastern part of the county where the ISIS militants have been operating since last year.
Syria's antiquities chief Maamoun Abdul Karim previously called on US-led coalition forces to save Palmyra’s ancient ruins and monuments from the destruction by the ISIS militants. That possibility seems likely as the the group has already destroyed similar archaeological sites and museums in Iraq.
ISIS militants destroyed the ruins of the Assyrian city of Nimrud and artifacts in the Mosul Museum earlier this year, a move that sparked outrage from the international community.
ISIS captured the Syrian Province of Raqqa, declaring it the capital of their self-proclaimed “caliphate” in June 2014 after seizing swathes of territory in Syria and Iraq.
A US-led coalition started air strikes in Syria and Iraq against ISIS targets last September.
The war in Syria started in 2011 in the form of anti-government demonstrations, but descended into a civil war between five main factions - the regime, the opposition, Al Qaeda affiliate Nusra Front, ISIS, and the Kurdish YPG militia.
Over four years of fighting has left over 230,000 Syrians dead, according to UN estimates.
More than 6.7 million are displaced internally while at least 5 million have fled the country to the neighbouring countries of Turkey, Lebanon, Egypt and Jordan.