The slaughter of Palmyra's citizens begins: First images emerge from Syrian city over-run by ISIS... and show rows of people beheaded as terror group celebrates freeing Islamists from state prison 

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Shocking images emerged today showing decapitated bodies strewn across blood-filled streets in Palmyra – victims of the Islamic State's unrelenting savagery as they stormed the ancient city.

The terror group have now seized full control of the historic settlement, putting the world heritage site and its priceless 2,000-year-old artefacts at risk of destruction.

The jihadis have also captured the military air base, intelligence headquarters and its notorious prison, where hundreds of inmates have reportedly been liberated.

British-based monitoring group, the Syrian Observatory for Human Rights (SOHR), said ISIS now controlled half of all territory in the war-torn country.

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Seized: Smoke rises over the ancient ruins of Palmyra as the Islamic State takes full control of the city after violent clashes with pro-government forces, the first time it has claimed a city from President Assad's regime

Butchered: Horrific images posted online show decapitated bodies strewn across a street, victims of the terror group's unrelenting savagery as they rampaged through the city

Jail break: This picture shared on several pro-ISIS Twitter account claims to show prisoners celebrating with their liberators after being freed from the notorious Tadmur prison by ISIS fighters in the city of Palmyra

Pro-government forces beat a hasty retreat late last night after 100 fighters were slaughtered in violent clashes in just a few hours.

It is the first time ISIS has claimed a city directly from the Syrian army and allied forces, which have already lost ground in the northwest and south to other insurgent groups in recent weeks.  

Beibares Tellawi, an activist in Homs province, said the militants had reached Tadmur prison, where thousands of Syrian dissidents have been imprisoned and tortured over the years.

The fate of the prisoners was not immediately known, although pro-ISIS Twitter accounts shared a image claiming to show inmates celebrating with militants after being set free. 

The jihadis have also seized control of the Jazl oil field in the Homs countryside.

Government war planes responded by carrying out air strikes on ISIS positions in the city.  

Rami Abdulrahman, the head of SOHR, who bases his information on a network of sources on the ground, said there were so far no reports of destruction of the city's historic artefacts. 

The city is home to a UNESCO World Heritage site, including ancient temples and colonnaded streets, which previously attracted thousands of tourists.  

Driven out: Pro-government forces have withdrawn after 100 fighters were killed in clashes overnight

Syrian state TV said pro-government forces managed to secure safe exit for most of the civilian population

Syria's antiquities chief said previously the insurgents would destroy ancient ruins if they took control of it. 

He said the group was in control of a hospital in the city which Syrian forces had used as a base before withdrawing.  

'The situation is very bad,' Syria's antiquities chief, Mamoun Abdulkarim, said after ISIS captured a northern section of the city earlier in the day.

'If only five members of ISIS go into the ancient buildings, they'll destroy everything,' he added, calling for international action to save the city.  

Syrian state TV reported that pro-government forces had managed to secure safe exit for most of the civilian population. 

The jihadists sparked international outrage this year when they blew up the ancient Assyrian city of Nimrud and smashed artefacts in the museum of Mosul, both in Iraq. 

Archaeological jewel: The city is home to a UNESCO World Heritage site and Syria's antiquities chief has said the insurgents would destroy ancient ruins if they took control of it

Under threat: Hundreds of statues and artefacts from Palmyra's museum have been transferred out of the city

Hundreds of statues and artefacts from Palmyra's museum have been transferred out of the city, according to Abdulkarim, but many others – including massive tombs – could not be moved. 

News of Palmyra's fall came after a State Department official said the weekend loss of Ramadi had prompted the U.S take an 'extremely hard look' at its strategy to confront the extremists.

The fall of Ramadi, their most significant victory since mid-2014 when they conquered swathes of land, sparked a US-led air campaign to support Baghdad. 

On Wednesday, the Anbar police chief was dismissed, after video footage emerged online suggesting security personnel deserted their posts at the height of the ISIS offensive. 

Facing destruction: Frescoes in the tomb of three brothers in the Valley of Tombs in Palmyra

A Marble altar depicting the Goddess Allat with a lion from the Temple of Baal Shamin in Palmyra, Syria

Prime spot: The ancient city of Palmyra stood on a caravan route at the crossroads of several civilisations and is now at the edge of an into which ISIS has moved

The militants' gains have sparked international concerns, with France pledging Wednesday to host high-level international talks next month in Paris over the threat posed by IS.

Middle East expert Hassan Hassan, writing in the Foreign Policy magazine, warned the fall of the Ramadi 'marks a dangerous new phase of the war' and would have a 'ripple effect across both the Syrian and Iraqi battlefields'.

The U.S. official said Washington would step up its aid to Iraq, including sending 1,000 anti-tank missile systems to help stop suicide car bombs and accelerating its training and equipping of tribal forces to fight ISIS.

'You'd have to be delusional not to take something like this and say: 'What went wrong, how do you fix it and how do we correct course to go from here?',' the official told reporters.   

Philistine: An ISIS militant smashes relics in Nimrud, Iraq, an Assyrian city dating back to the 13th century

Asking not to be identified, the official highlighted the ISIS tactic of ploughing huge 'vehicle-born improvised explosive devices' (VBIEDs) into buildings and walls.

In Ramadi, an explosives-packed bulldozer was used to blow up the security perimeter around a government-held compound.

Around 30 vehicles such as Humvees then flowed in, 10 of which were carrying enough bomb-making materials to carry out explosions the size of the blast of the 1995 Oklahoma City bombing. 

Besides the more than 3,000 air strikes carried out so far, Washington has supported a deep reform of Iraq's army and offered training to Sunni tribesmen.

But that failed to prevent the loss of Ramadi, where militias backed by US arch-foe Iran will now take the lead in any counter-attack. 

During a visit to Baghdad on Wednesday, Iranian Defence Minister Hossein Dehghan stressed Tehran's commitment to Iraqi unity but also emphasised Iran's role in the fight against ISIS.

According to officials from Anbar, at least 500 people were killed in three days of fighting in Ramadi during which IS used waves of suicide car bombs.

The army's retreat was chaotic, once again raising questions over the credibility of Iraq's regular forces.

Tens of thousands were forced to flee their homes in the process.

And on Wednesday, more than 2,000 were able to join them and escape conflict-torn Anbar after the authorities opened a bridge that had been closed for three days. 

HISTORY OF PALMYRA AND THE REBELLIOUS QUEEN WHO DEFIED ROME 

Palmyra was once the seat of Queen Zenobia, who ruled over the Palmyrene empire in the 3rd century.

She expanded its reach, conquering, expelling and then beheading the Roman prefect in Egypt.

Zenobia ruled over Egypt until 271, when she was defeated and taken as a hostage to Rome by Emperor Aurelian.

The queen claimed descent from the Macedonian kings of Egypt and was a descendent of Cleopatra.

The blending of cultures she embodied earned Palmyra its status as a Unesco world heritage site.

Rebellious: 'Queen Zenobia Addressing Her Soldiers' by Giovanni Battista Tiepolo. The Palmyrene queen led a rebellion against the Romans

Palmyrene statues and reliefs on civic buildings and in tombs, depict women sporting distinctive hairstyles, clothing and jewellery.

Most of these have long since been transported from the on-site museum to undisclosed locations for safekeeping.

The city was a staging post along the Silk Road for camel caravans plying between Antioch on the Mediterranean and Doura Europos on the Euphrates.

Syrian rebels held the site from February to September 2013 before the regime recaptured it.

One of the ancient city's masterpieces, the Temple of Baal, suffered some damage during the accompanying artillery exchanges.