russian warplanes bomb Palmyra
Footage shows a target hit during a Russian air raid in SyriaRussian Defense Ministry

A fortification, an underground bunker and anti-aircraft guns were destroyed by Su-25 Russian jets in positions around the ancient Syrian city of Palmyra, according to Moscow. Activists also said the air strikes concentrated close to a 13th-century castle to the west of Palmyra's ruins which date back over 2,000 years.

"Su-25 jets hit a fortified IS position in the Tadmur area of Homs province," Russia's defense ministry said in a statement, using the Arabic name for Palmyra.

"As a result of a direct strike, a fortification, an underground bunker and anti-aircraft artillery were destroyed."

The Russian defence ministry did not give out information on when the attack on Palmyra took place but Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, said that Russian planes had targeted Palmyra with strikes on Monday. He said several strikes hit the city's ancient citadel, but could not give any more details.

However, the seriousness of the damage was difficult to assertain. Khaled al-Homsi, an activist from Palmyra, also reported Russian strikes on the citadel on the western edges of the Unesco World Heritage site. "The extent of the damage could not be verified," he told AFP.

Nasser al-Thaer, an activist in Palmyra told AP that at least eight airstrikes struck the area of the castle, sending smoke and clouds of dust high up into the sky. The 13th-century fortification is known as Qalaat Shirkuh or Qalaat Ibn Maan, and is part of the Unesco World Heritage site. The stronghold was built on a hilltop about 150m above the main ruins.

Last month, the Association for the Protection of Syrian Archaeology reported that parts of the castle had been damaged in Syrian government barrel bomb attacks, according to the BBC.

Russia also claims that its jets have struck over 237 targets in Syria over the past two days. Warplanes have targeted sites belonging to "terrorist groups" including Islamic State and al-Qaida affiliate Nusra Front in the Homs, Hama, Latakia, Damascus, Aleppo and Raqqa provinces, Moscow said in a statement.

IS militants have destroyed two 2,000-year-old temples, an arch and funerary towers since forcing Syrian government troops out of Palmyra in May.