Detailed footage of the devastation caused by Islamic State militants inside Syria's ancient city of Palmyra has been revealed.

The new video shows the world heritage site reduced to rubble as a result of the extremists waging war on the famous landmarks over the past year.

Syrian government forces finally drove ISIS out at the weekend, inflicting what they described as a "mortal blow" to the terror organisation.

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

But Syria's antiquities chief says priceless artefacts have survived better than feared from a campaign of destruction which UNESCO described as a war crime.

"We were expecting the worst. But the landscape, in general, is in good shape," Maamoun Abdulkarim said from Damascus.

"We could have completely lost Palmyra ... The joy I feel is indescribable."

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

Russian forces were heavily involved in the fight to retake the city, with warplanes carrying out around 40 sorties, striking 117 "terrorist targets" and killing 80 ISIS fighters, Moscow's defence ministry said.

The Syrian army said the city would now serve as a base to "broaden operations" against ISIS, including in its stronghold of Raqqa and Deir Ezzor further east.

The ancient city, north-east of Damascus, drew some 150,000 tourists a year before Syria's civil war and is known to Syrians as the "Pearl of the Desert".

ISIS and its jihadist rival, the Al Qaeda-affiliated al Nusra Front, are not party to a ceasefire in force across Syria since 27 February.

The truce has brought relative quiet to many areas across Syria, where more than 270,000 have been killed and millions have fled their homes in the last five years.

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