Chemical weapons experts say mustard gas was used in a Syrian town where ISIS was battling a rebel group.
“If the international community had instituted the no-fly zone, Aleppo would be free today.”
Cluster bombs are a reliable method for killing noncombatants outside an intended target field.
Putin may have insisted on new Iranian forces before committing his air force.
It will be the first time that Tehran attends an international summit on the four-year-long war.
Putin spoke a day after Assad made a surprise visit to Moscow for talks with the Russian leader.
The Syrian leader's visit came just three weeks after Moscow's airstrike campaign began.
Assad is more confident in his regime's strength, and the Kremlin seeks to heighten its diplomatic cred.
Assad flew to Moscow on Tuesday evening to thank Putin personally for his military support.
Russia is concerned about the loyalty of its own large Islamic community, which, like ISIS, is largely Sunni.
The government in Havana called the allegations "irresponsible and unfounded."
Obama said the Syrian civil war could only end with a political solution leading to a new inclusive government.
Government troops and their allies backed by Russian jets have launched an offensive against rebels near Aleppo.
The offensive builds on over a week of ground attacks launched with Russian air support.
Bringing Russia in to bolster Assad’s regime could risk Iran’s strategic command of the situation in Syria.
Gains by ISIS north of Aleppo would threaten the supply lines of rival rebels inside the city.
The death of Hossein Hamedani may disrupt Iranian efforts in Syria.
Bush said Vladimir Putin was exploiting a vacuum of U.S. leadership in Syria and elsewhere.
The offensive, which both officials said would begin soon, would expand on a ground attack by the same alliance.
Though Putin may look like he’s in control in Syria, the intervention is likely to end badly for him.
The move came weeks after Moscow raised the stakes with its intervention in the long-running civil war.
The new alliance calls itself the Democratic Forces of Syria.