ISIS militants have destroyed the historic Tetrapylon and 'significantly damaged' the Roman Theater at the UNESCO World Heritage site of Palmyra, in Syria.

Satellite images, taken on January 10, show the monuments of huge cultural importance lying in ruins after the jihadist group recaptured Palmyra on December 11, 2016, when Syrian armed forces pulled out.

The ASOR Cultural Heritage Initiative (ASOR CHI), which documents the cultural heritage of Syria and northern Iraq, said: 'ISIL executed prisoners around the archaeological site, destroyed the Tetrapylon and part of the Roman Theater.'

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This satellite image, taken on January 10, shows the significant damage caused to the Roman Theater and Tetrapylon (noted with red arrows) in the UNESCO World Heritage site of Palmyra

This satellite image shows the Tetrapylon and Theater prior to recent damage. The photo was taken on December 26, 2016

The Tetrapylon in Palmyra was once a grand platform with four columns at each corner topped by a massive corinth. It is pictured before it was blown up by ISIS

The damage to the ancient structures occurred between December 26, 2016 and January 10, 2017, ASOR CHI said.

'The Tetrapylon appears to have been intentionally destroyed using explosives. Two columns remain standing, but the majority of the structure has been severely damaged and column drums and debris are visible on the ground around the structure,' it said.

'The Roman Theater has sustained damage to the stage backdrop, primarily in the area of the Porticus. New stone debris is scattered across the center of the stage,' ASOR CHI added.

ISIS terror chiefs sparked a global outcry when they started destroying Palmyra's treasured monuments, which they consider idolatrous, after first taking the city in May 2015.

The unfinished Roman amphitheatre (pictured before it was damaged by ISIS), which dates back to the 2nd century CE, contained low level seating reserved for the elite

The UNESCO World Heritage Site of Palmyra is pictured with a red box denoting the area of new damage. The Temple of Bel and Baal Shamin were previously destroyed by ISIS

Palmyra: Syria's 'Bride of the Desert' Palmyra, situated about 130 miles northeast of Damascus, is known by Syrians as the 'Bride of the Desert'. It was an important caravan city of the Roman Empire, linking it to India, China, and Persia. Before the outbreak of Syria's conflict in March 2011, the UNESCO site was one of the most popular tourist attractions in the Middle East drawing 105,000 visitors a year. A picture taken on March 14, 2014, shows the famous Arch of Triumph (front) and a partial view of the ancient oasis city of Palmyra. Islamic State extremists have since blown up the famous Arch of Triumph Tourists take pictures at the ancient Palmyra theater on April 18, 2008, before the war in Syria broke out The whole of Palmyra, including the four cemeteries outside the walls of the ancient city, has been listed as a world heritage site by UNESCO since 1980. Global concern for Palmyra's magnificent ancient ruins spiked in September 2015, when satellite images confirmed that ISIS had demolished the famed Temple of Bel as part of its campaign to destroy pre-Islamic monuments it considers idolatrous. Unesco described the temple as one of the best preserved and most important religious edifices of the first century in the Middle East. In October last year, the jihadists blew up the Arch of Triumph, dating from between 193 and 211 AD, as they pressed a campaign of destruction that Unesco has said constitutes a war crime punishable by the International Criminal Court. Advertisement

The terrorists dynamited the Palmyra temples of Baal Shamin and Bel, as well as funeral towers and a triumphal arch, which had stood for 1,800 years in the oasis city described by the U.N. cultural agency as a crossroads of cultures since the dawn of humanity.

The group used Palmyra's ancient theatre as a venue for public executions and also murdered the city's 82-year-old former antiquities chief.

The now obliterated Tetrapylon was once a grand platform with four columns at each corner topped by a massive corinth, built to make the main route through Palmyra appear more harmonious.

'This type of Tetrapylon is called a tetrakionion, in which the four corners of the structure are not connected overhead,' ASOR CHI explained.

Each of the four groups of pillars in the tetrapylon supports 150,000kg of solid cornice.

Before it was destroyed by ISIS only one of the original pink Egyptian granite columns was still standing - the others were modern reproductions.

A plume of smoke rises over the Baalshamin temple in Palmyra in a photo released on August 25, 2015 on a social media site used by Islamic State militants. Arabic at bottom reads, 'The moment of detonation of the pagan Baalshamin temple in the city of Palmyra'

Residential neighbourhoods in the adjacent modern town, where 70,000 people lived before the war, were found deserted and damaged when the Syrian army recaptured Palmyra last year

Syrian soldiers stand on the ruins of the Temple of Bel in the historic city of Palmyra after reclaiming it from ISIS last year

Government army soldiers climb their way to the top of Fakhr al-Din al-Maani Citadel last year to place a flag

Destroyed statues at the damaged Palmyra Museum are pictured on Monday, March 27, 2016, after the Syrian army reclaimed the city

Many sculptures (for example the one pictured) were destroyed by ISIS but a secret deal between the government and ISIS bosses may have led to some treasures being saved last year

Palmyra (pictured here before it was captured by ISIS) is an ancient city of Semitic origin that dates back into prehistory. It was known as caravan stop for travellers crossing the Syrian Desert back in the second century BC. The city is mentioned in the Bible as Tadmor in to chronicles

Meanwhile, the unfinished Roman amphitheatre, which dates back to the 2nd century CE when Palmyra was once one of the most important cultural centres of the ancient world, contained low level seating reserved for the elite.

It was one of the best preserved Roman theatres in Syria and is 'ringed by a colonnaded portico which opens onto a colonnaded street leading to Palmyra's Southern Gate,' ASOR CHI said.

The UN on Friday led condemnation of attacks calling the destruction a 'war crime' and 'cultural cleansing.'

In a statement, Irina Bokova, director general of the Paris-based UN cultural agency UNESCO, described the wrecking as 'a new war crime and an immense loss for the Syrian people and for humanity.'

'This new blow against cultural heritage... 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,' Bokova said.

Moscow on Friday deplored the new destruction, with President Vladimir Putin's spokesman Dmitry Peskov calling it 'a real tragedy from the point of view of cultural and historical heritage.'

Asked whether the Russian military is likely to step in to recapture Palmyra for a second time, Peskov said only that: 'Russian military continues to support the Syrians in battling terrorists.'

For his part, Russian Foreign Minister Sergei Lavrov, calling those who demolish world treasures 'barbarians', added: 'Such ideology and practice have absolutely no place in modern civilisation.'

Also Friday, UNESCO said years of conflict in Syria had 'totally destroyed' 30 percent of the historic Old City of Aleppo - named a World Heritage Site in 1986 - and around 60 percent of the quarter was 'severely damaged.'

The mission reported 'extensive damage' to the Citadel, a fortress dating to the first millennium BC, and the Great Mosque of Aleppo, the largest and one of the oldest of the city's mosques.

The loss of east Aleppo was the biggest blow to Syria's rebel movement in the nearly six-year conflict, which has killed more than 310,000 people.

Last year International Criminal Court judges jailed a Malian jihadist for nine years for demolishing Timbuktu's fabled shrines in the first such case to focus on cultural destruction as a war crime.