This is the first time Russian President Vladimir Putin received Syrian leader Bashar al-Assad in Moscow since 2015.
And at their meeting on Monday (September 13), Putin criticized foreign forces that are in Syria without a U.N. mandate -- a reference to American and Turkish troops.
"The main problem in my view is that foreign military forces without the permission of the U.N. and without your sanctioning are present on some territories of the country. Which contradicts international law. And does not give you an opportunity to use maximum efforts for the consolidation of the country, and to move on the path of its restoration as fast as you could if the whole territory of the country was controlled by the legal government."
Assad thanked the Russian leader for humanitarian aid to Syria and for his efforts to halt, quote, "spread of terrorism."
Russia is Assad's most powerful ally in the decade-long Syrian conflict.
Russia's air force played a critical role in turning the tide in Assad's favour after it deployed there in 2015, helping him recover most territory lost to insurgents.
However, significant parts of Syria remain out of state control, with Turkish forces deployed in much of the north and northwest - the last major bastion of anti-Assad rebels.
U.S. forces are also still in the Kurdish-controlled east and northeast.
Meanwhile, on Tuesday, a day after the meeting with Assad, Putin started self-isolating after members of his entourage fell ill with COVID-19.
The leader has been forced to cancel some foreign travel as a result.