In this photo released by the Syrian official news agency SANA, Syrian soldiers gather around a Syrian national flag in Palmyra, Syria, Sunday, March 27, 2016.

Russian President Vladimir Putin on Sunday spoke by phone with Syrian President Bashar al-Assad, congratulating him on his forces retaking Palmyra, the Kremlin said.

“In a conversation with the Syrian president, Vladimir Putin congratulated his colleague on Syrian forces liberating the city of Palmyra from terrorists, noting the importance of preserving this unique historic city for world culture,” Kremlin spokesman Dmitry Peskov said, quoted by RIA Novosti state news agency.

According to Russia’s Interfax news agency, the Kremlin spokesman said Assad told Putin that Palmyra’s recapture would have been impossible without Russia’s help.

Syrian government forces on Sunday retook all of the ancient central city of Palmyra from ISIS, opening up a path into the militant group’s eastern heartlands of Raqqa and Deir Azzor.

‘Fresh proof’

Hailing the victory, Syrian President Bashar al-Assad said publicly that the retaking of Palmya was an “important achievement.”

“This is an important achievement and fresh proof of the efficiency of the Syrian army and its allies in fighting terrorism,” Assad said of the recapture of Palmyra, during a meeting with French parliamentarians in Damascus.

A statement read out on Syrian television said that the recapture of Palmyra from ISIS also showed that Syrian government forces and their allies were the only force capable of defeating terrorism in Syria.

It said the army and its allies, backed by Syrian and Russian air forces, would continue their campaign against ISIS, the Nusra Front “and other terrorist groups”.

The Syrian government has described all armed factions fighting President Bashar l-Assad as terrorist groups.

It was earlier reported that Syrian regime forces advanced into Palmyra on Saturday with heavy support from Russian air strikes, taking control of several districts in a major assault against ISIS fighters, Syrian state media and a monitoring group said.

Television footage showed waves of explosions inside Palmyra and smoke rising from buildings, as tanks and armored vehicles fired from the outskirts.

The Syrian Observatory for Human Rights said it was the biggest assault in a three-week campaign by the Syrian army and allied militia fighters to recapture the desert city and open up the road to ISIS strongholds further east.

Observatory director Rami Abdulrahman said Syrian soldiers and allied militias had taken control of one-third of Palmyra, mainly in the west and north, including part of the ancient city and its Roman-era ruins. Soldiers were also fighting on a southern front, he said.

Syrian media and Arab television channels broadcasting from the slopes of Palmyra’s mediaeval citadel, one of the last areas of high ground seized by the army on Friday, said troops had advanced inside Palmyra and had taken several neighborhoods.

The recapture of Palmyra, which the extremist group seized in May 2015, would mark the biggest reversal for ISIS in Syria since Russia’s intervention turned the tide of the five-year conflict in Assad’s favor.

The group and al-Qaeda’s Syrian branch the Nusra Front are excluded from a month-long cessation of hostilities that has brought a lull in fighting between the government and rebels battling Assad in western Syria.

The limited truce has allowed some aid deliveries to get to previously inaccessible areas under siege.

The International Committee for the Red Cross said on Saturday it brought food and hygiene items to three areas of south Damascus the day before.

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