The perpetrators of war crimes and crimes against humanity must not go unpunished.
Sending Russian forces to Syria is a distraction from the problems Putin has with Ukraine.
American officials told The Wall Street Journal that Putin’s primary military goal was supporting the Assad regime.
The strikes seemed to have been carried out near Homs, an area crucial to Assad's control of western Syria.
Adel al-Jubeir said that Assad must either leave voluntarily or face being forced to step down.
Some of the U.S.-trained rebels handed over some of their equipment to Nusra last week in return for safe passage.
"I side with the group that says 'if Russia wants to go and fight ISIS, you should let them,'" Trump said.
Western governments should be warned that including Assad will only prolong the conflict.
The president is calling for a new leader to replace Syrian President Bashar Assad to help defeat ISIS.
The two leaders are to hold face-to-face talks on the Syrian conflict on Tuesday.
A no-fly zone to stop Assad’s chemical barrel bombs? Then what?
Kerry said the Obama administration hopes talks between Russia and the U.S. will take place soon.
Russia’s recent military support of Syria is more about Ukraine than the Middle East
The army had been trained in the use of the weapons in recent months and was now deploying them.
Moscow has come under increased international pressure in recent days to explain its moves in Syria.
U.S. officials suspect Russia is reinforcing to aid Assad, Moscow's ally since the Cold War.
The White House has warned that any support for Assad is 'destabilizing and counterproductive.'
Assad knows the rebels’ backers are not interested in a decisive rebel victory.
The Syrian president says Russia is reliable, unlike "backstabbing" United States.