Moscow's angry statement came in response to accusations by Prince Saud al-Faisal, the Saudi foreign minister, that Russia was responsible for mass killings in Syria because of its military support for the regime.
"Of course, we are not going to justify ourselves before anyone. Our fundamental position on Syria is well known," the Russian foreign ministry said in a statement.
"At the same time, a number of capitals, including Riyadh, unfortunately are not ashamed of employing all sorts of methods and contacts, including by financing and arming international terrorists and extremists," the ministry statement said.
Syrian President Bashar al-Assad refers to the armed opposition as terrorists, a position supported on occasion by Moscow.
Russia supplies its strategic Middle East ally with weapons under contracts signed before the conflict broke out in March 2011.
It has also blocked a series of UN Security Council resolutions condemning Assad for the violence, which a British-based monitor said has now claimed more than 100,000 lives.