Forces loyal to the Syrian regime amassed outside the ancient city of Palmyra on Wednesday, preparing to wrest it back from Islamic State (IS) militants.

The extremist group overran the area in May 2015, seizing its modern town, UNESCO-protected ruins, and a prison so notoriously brutal that it was once described as the "kingdom of death and madness."

Although pro-government media outlets had claimed for months that President Bashar al-Assad's army was on the verge of recapturing the city, it has taken a fresh offensive backed by Russia and Iran to turn that claim into reality.

"At this stage, I look to the involvement of the regime's allies — the Russian air and ground troops and Iran-backed militias — as a way of gaging how serious an operation is," said Chris Kozak, an analyst at the Institute for the Study of War who specializes in mapping Syria's conflict.

Assad's army has all but collapsed under the pressures of its five-year war, leaving his foreign backers in control of the fight across key battlefronts.

Experts said that Russia's deepening involvement in the fight for Palmyra, coming just over a week after President Vladimir Putin announced the partial withdrawal of his troops from Syria, points to a short-term shift in the country's fighting priorities.

With the fight against opposition groups largely on hold thanks to an internationally brokered ceasefire, Russia is turning its attention to IS, the group whose threat Putin initially used to justify military intervention back in September.

"From Putin's perspective, this is the time to turn attention to the Islamic State," said Kozak. "While the cessation of hostilities means fighting is largely neutralized on other fronts, this is a very clear way to show the Europe that it's genuinely interested in fighting Islamic State."

Palmyra's recapture would also be a strategic victory. He who rules the oasis city will also control its surrounding desert, an area of some 12,000 square miles extending to the Iraqi border — and bring protection to the largely regime-cities of Homs, Hama, and Damascus to the west.

Moscow said this week that it was flying up to 25 sorties a day in support of government forces in the Palmyra countryside. There were also suggestions that Russian special forces were involved in the battle: IS boasted last week that it had killed five of Moscow's soldiers, at least one of whom appeared to have been involved in bomb disposal.

Local reports also suggested this week that Iran, a key regime ally, had sent elite forces and an Afghan-dominated militia to the Palmyra area.

In response, IS fighters appeared to be putting up a fierce fight, killing at least 26 pro-government fighters on Monday alone, according to the Syrian Observatory for Human Rights, a UK-based monitoring group.

"They're telling us all to stay in our houses. The noises are terrible," one resident, who asked not to be named out of fear for his family's safety, told VICE News. "It feels like a battle for the end of the world."

Another, identified as Khaled, told Syria Direct that IS front-lines were largely being manned by teenagers, following heavy losses in earlier pitched battles and airstrikes.

"We are seeing hundreds of rockets and shells a day, either from planes or ground artillery and mortars," he said. "This bombardment has flattened entire neighborhoods."

This is only Moscow's second concerted attempt to take on IS, after an earlier intervention to break the militants' long-standing siege on a regime air base in east Aleppo last year.

Human rights groups have instead accused Russia of focusing the majority of its firepower on opposition-held areas, many of them heavily populated. Hundreds of civilians have been killed in the air raids and hospitals appear to have been deliberately targeted.

Victory in Palmyra would be deeply symbolic. The IS takeover of the city and its ancient ruins horrified international observers, generating wall-to-wall media coverage of the regime's collapse in the face of the extremist group's advancing army.

The resident who spoke to VICE News described the militants' rule as a 'lifetime of hell'

They have ruled the city with an iron fist. Its sandy amphitheater, one of the ancient panorama's most famous sites, has been repurposed as a stage for executions. Public squares have been turned into forums from which the militants trumpet their latest diktats, and many of the ancient ruins — once part of the most complete panorama to survive classical antiquity — have been blown to smithereens.

The resident who spoke to VICE News described the militants' rule as a "lifetime of hell." In the family's moments of greatest fear, he said that his 16-year-old daughter had spoken of suicide, a deep taboo in Arab societies. "I'm not ashamed to say we're scared anymore. How could I say otherwise? Bashar is our only hope now," he said, referring to the Syrian president.

Assad's fate has been a key obstacle in ongoing peace talks, with the government insisting any discussion of him leaving is "excluded" and the opposition saying suggestions he might remain are "unacceptable."

Kyle W. Orton, an associate fellow at the Henry Jackson Society, said that Palmyra's recapture could bolster Assad's claim to be the most important defender of Syria's past, present, and future.

"The regime and Russia have already done terrific damage to the inhabited part of Palmyra, but the ability to pose among the ancient ruins after recapturing this piece of history from ISIS will help the pro-regime coalition's propaganda claim that Assad is the last line of defense for civilization," he said, using an alternative acronym for IS.

In footage broadcast by the Syrian Ikhbariya television station on Wednesday, a group of regime officers, apparently standing at the city's outskirts, broke into pro-government chants as their commander said: "God willing, within few hours we will enter and secure the town."