Russian Foreign Minister Sergey Lavrov has called on world powers to help arm the Syrian army which he described as the most efficient force against the Islamic State group.

The U.S. and NATO have raised concerns over Russia's military buildup in Syria since they see President Bashar Assad as the cause of the Syrian crisis, which has claimed more than 250,000 lives in over four years.

Moscow has sought to cast arms supplies to Assad's government as part of international efforts to combat Islamic State militants.

Lavrov said in Moscow on Friday that Russia would continue to supply Assad with weapons and called on other countries to help the Syrian government and its ground troops.