Russia flies both military equipment and humanitarian aid to Syria, Foreign Minister Sergei Lavrov has said.

The US and some European countries have expressed growing concern over the cargo on flights from Russia to Syria.

Moscow has previously insisted in public that its flights to Syria are only humanitarian.

Washington has put pressure on Greece and Bulgaria in recent days to deny Russia's requests to use their airspace for its Syrian flights.

This comes amid concerns from the US and Nato that Russia is increasing its military presence at a Syrian airfield.

Russia has backed Syrian President Bashar Assad throughout the country's four-and-a-half-year civil war, providing weapons and military experts to train Syria's army.

Mr Lavrov confirmed Russia has military personnel in Syria but said nothing about reported deployments of additional troops.

President Vladimir Putin has not ruled out a bigger role in Syria. Asked last week if Russia could deploy its troops to Syria to help fight Islamic State, he said Russia was "looking at various options".

Mr Putin is expected to focus on the situation in Syria when he addresses the United Nations General Assembly at the end of the month.