At least 370 people including civilians were killed in Russia's so-called 'precision' airstrikes claimed to be targeting the Islamic State (Isis) militants, according to a UK-based monitoring agency.

According to Syrian Observatory for Human Rights (SOHR), 243 militants, part of terrorist outfits such as Nusra, Isis and other Islamist factions have been killed in the Russia airstrikes in Syria.

However, there has also been high civilian casualty, SOHR said. At least 127 civilians including 36 children and 34 women were killed in the Russian aerial attacks claimed to have been carried on terrorist targets in Syria.

SOHR, which collects information from several ground sources in Syria, in a statement on its website, accused the regime and Russian air forces of bombing areas without distinguishing between the civilian and militant targets.

The monitoring group also has asked UN Security Council to issue an order to stop the military operations in Syria.

Russia launched a massive air campaign in Syria on 30 September and since then, Moscow has claimed that it has destroyed dozens of militant facilities belonging to Isis and Al Qaeda's Nusra Front. 

According to IHS Jane's, a respected military intelligence website, Russia is spending $4 million every day in Syria for its military efforts that will keep Syrian ruler Assad in power. 

The reports about civilian casualties have come just as Syrian president Bashar al Assad arrived in Moscow on Tuesday to thank Russian President Vladimir Putin for his military support. 

The Syrian President arrived in Moscow on Tuesday evening, in a closely guarded surprise visit.

"First of all I wanted to express my huge gratitude to the whole leadership of the Russian Federation for the help they are giving in Syria," Assad told Putin, Reuters reported.

"If it was not for your actions and your decisions the terrorism which is spreading in the region would have swallowed up a much greater area and spread over an even greater territory," Assad said during his first foreign visit since the start of the Syrian conflict in 2011.