Russian President Vladimir Putin on Sunday congratulated his Syrian President Bashar al-Assad on recovering the ancient city of Palmyra, according to state news agency SANA.

SANA said Putin, whose air force played a crucial role in supporting the Syrian army, congratulated Assad by phone on liberating Palmyra from the grip of the Islamic State (IS) militant group. Putin promised ongoing Russian support to Syria's army.

Assad said the Syrian army's determination and the "efficient" support of Russia's air force were behind the recovery of Palmyra.

He said earlier that the military's recovery of Palmyra demonstrated the Syrian army and its allies' efficient strategy in the war on terror.

He added that Syria and Russia's effective strategy is markedly prominent when compared with the U.S.-led coalition.

The Syrian Army's General Commander said that defeating the IS in Palmyra is just the beginning of an anticipated domino effect leading to the militant group's total collapse.

"Recapturing Palmyra dealt IS a strong blow and will most certainly destroy the group's morale, thereby launching its final collapse," the Syrian army said in a statement.

The recovery of Palmyra, the statement added, "demonstrated that our army in cooperation with our allies are the main powers capable of eradicating terrorism."

The military's statement referred to both the Russian and Syrian air forces' efficient help in recapturing the ancient city.

Meanwhile, the state-run Alekhbaria news agency said the three-week armed conflict in Palmyra killed over 600 IS militants, whereas the UK-based Syrian Observatory for Human Rights said the troops killed over 400 militants.

Activists added that the campaign killed 180 Syrian soldiers.

A military source told Xinhua that the IS withdrew from the city under heavy attack and shelling by the Syrian army.

The source, who spoke on condition of anonymity, said the IS retreated towards the town of Sukhneh, east of the central province of Homs.

The source then confirmed that the ancient city of Palmyra is booby-trapped and that bomb squads have started working.

Palmyra was captured by the IS last May, after which the Syrian army started a comprehensive assault campaign to recover it.

Since occupying Palmyra last May, the IS destroyed the city's military prison along with several Islamic tombs. It also publicly executed soldiers and individuals accused of working for the government.

The ancient city of Palmyra contains monumental ruins of a great city that was once one of the ancient world's most important cultural centers.

Syria is endowed with several prehistoric Greek, Byzantine and Islamic roots.

Syria used to attract numerous multinational archaeological missions seeking new clues and investigating historical facts concerning the development of civilizations before the crisis.