MOSCOW/BEIRUT (REUTERS, AFP) - Destruction by Islamic State in Iraq and Syria extremists at Syria's ancient city of Palmyra is a "real tragedy" for the world's cultural treasures, President Vladimir Putin's spokesman Dmitry Peskov said Friday (Jan 20).

"What is happening (in Palmyra) is a real tragedy from the point of view of cultural and historical heritage," he told journalists.

"Barbaric actions of the terrorists are continuing."

Palmyra, an ancient site in central Syria with famous Unesco-listed temples, was overrun by ISIS before being seized in a Russia-backed offensive in March.

However, ISIS took control of the area again late last year and Syria's antiquities chief said Friday that the terrorist group has destroyed Palmyra's 3rd century AD tetrapylon and that the amphitheatre was damaged.

The Tetrapylon, marking a slight bend along Palmyra's grand colonnade, comprises a square stone platform with matching structures of four columns positioned at each of its corners.

Satellite imagery sent by Abdulkarim to Reuters showed it largely destroyed, with only four of 16 columns still standing and the stone platform apparently covered in rubble.

The imagery also showed extensive damage at the Roman Theatre, with several towering stone structures destroyed on the stage.

Abdulkarim said if ISIS remained in control of Palmyra "it means more destruction". He said the destruction took place sometime between Dec 26 and Jan 10, according to the satellite imagery of the site.

ISIS put 12 people to death in Palmyra earlier this week, some of them execution-style in the Roman Theatre.

Just last May, a famous Russian orchestra performed at the theatre after Palmyra was first won back from ISIS.

Asked whether the Russian military is likely to step in to recapture Palmyra for the second time, Peskov merely said, "Russian military continues to support the Syrians in battling terrorists."

Russian Foreign Minister Sergei Lavrov called those who demolish world treasures "barbarians."

"Barbarians will be barbarians," he said during a press conference in Moscow. "Such ideology and practice have absolutely no place in modern civilisation."

The head of the United Nations cultural agency said the Palmyra destruction was a "new war crime".

"This destruction is a new war crime and an immense loss for the Syrian people and for humanity," Unesco Director General Irina Bokova said in a statement.

"This new blow against cultural heritage, just a few hours after Unesco received reports about mass executions in the theatre, shows that cultural cleansing led by violent extremists is seeking to destroy both human lives and historical monuments in order to deprive the Syrian people of its past and its future."

ISIS had previously captured Palmyra in 2015. It held the city for 10 months until Syrian government forces backed by allied militia and Russian air power managed to drive them out last March.

During its previous spell in control of Palmyra, ISIS destroyed other monuments there, including its 1,800-year-old monumental arch. Palmyra, known in Arabic as Tadmur, stood at the crossroads of the ancient world.

Russia marked the capture of Palmyra from ISIS by sending the Mariinsky Theatre to perform a surprise concert, highlighting the Kremlin's role in winning back the city.

The concert, held just over a month after Russian air strikes helped push ISIS militants out of Palmyra, saw Valery Gergiev, a close associate of President Vladimir Putin, conduct the Mariinsky orchestra.

ISIS swept into Palmyra again in December when the Syrian army and its allies were focused on dealing a final blow to rebels in the city of Aleppo.

Eastern Aleppo fell to the government later that month.