Moscow - Russia released drone footage Monday showing new destruction in Syria's historic town of Palmyra, which was recently recaptured by the Islamic State group, and warned that the militants could be planning the further demolition of antiquities.The Russian Defence Ministry says Syrian government forces are advancing toward the town as another battle for the ancient site looms.The video showed that the militants have badly damaged the facade of the Roman-era amphitheatre and the Tetrapylon - a set of four monuments with four columns each at the centre of the colonnaded road leading to the theatre.The video appears to show that only two of the 16 columns remain standing.ISIS militants have destroyed ancient sites across their self-styled Islamic caliphate in Syria and Iraq, perceiving them as monuments to idolatry.Palmyra, a UNESCO world heritage site that once linked Persia, India and China with the Roman Empire and the Mediterranean, has already seen destruction at the hands of the ISIS group.The ancient town first fell to ISIS militants in May 2015, when they held it for 10 months. During that time, the extremists destroyed ancient temples and eventually emptied the town of most of its residents, causing an international outcry.The extremists were eventually driven out by Russian and Syrian government forces, but they seized the town again in December.Russia's Defence Ministry said in a statement on Monday that Syrian government troops advancing toward the city are about 20km away. It said Russian warplanes last week carried out more than 90 sorties to provide air cover for the offensive.It added that some 200 ISIS fighters have been killed and that Syrian forces destroyed 180 "infrastructure objects" and 15 ammunition depots.Bringing explosivesThe drone footage, which the Russian Defence Ministry said was filmed earlier this month, showed a central section of Palmyra's theatre lying in ruins.The ministry said its drones also recorded significant truck movements in the area around the archaeological site, which could mean that the ISIS militants are bringing explosives to the site.Maamoun Abdulkarim, the head of Syria's antiquities department, said last month that reports of the recent destruction first trickled out in late December. Satellite images surfaced in January.This photo combo, made from footage taken from the Russian Defence Ministry official website, purports to show the Tetrapylon, a set of four monuments with four columns each at the centre of the colonnaded road leading to a Roman-era amphitheater on June 6, 2016, left, and on Feb. 5, 2017, right, in Palmyra, Syria. (Russian Defence Ministry Press Service, via AP) The release of the video in Russia came as the Syrian government and the opposition prepared for a new round of peace talks later this month aimed at ending the country's nearly six-year civil war, which has killed hundreds of thousands of people and displaced millions.The Syrian government said on Monday it is ready to release prisoners in exchange for civilians or troops held by insurgents. Syrian state TV quoted an unnamed official as saying the offer comes ahead of a two-day meeting later this week in the Kazakh capital, Astana.Kazakhstan's Foreign Ministry has invited government and opposition officials, as well as delegates from Russia, Turkey, and Iran for preparatory talks in Astana on Thursday and Friday ahead of UN-brokered talks with the Syrian government planned for February 20 in Geneva.Last week the Syrian government and rebels exchanged dozens of people, including women and children who were held by insurgents for years.