According to a new report, almost all the city's physicians have fled, been killed or been detained during Syria's civil war.
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."
Putin spoke a day after Assad made a surprise visit to Moscow for talks with the Russian leader.
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.
Gains by ISIS north of Aleppo would threaten the supply lines of rival rebels inside the city.
The offensive, which both officials said would begin soon, would expand on a ground attack by the same alliance.
Islamic State fighters have seized villages close to the northern city of Aleppo from rival insurgents.
The terror group has captured five more villages in northern Aleppo, described as a 'major turning point' by analysts.
The fall of Aleppo would be a major blow for President Bashar al-Assad.
Militia of fully-veiled women fire AK47 rifles at world's oldest Byzantine church.
"If he was here, I would burn him by my hand. I wish to capture pilots and burn them," a young boy said at the event.
Some fighters, like Ahmed al-Hussein, care for entire packs of dogs.
Syrian actor urges President Bashar al-Assad to spend two minutes in the snow.
The British-based Syrian Observatory for Human Rights said a number of armed groups in Aleppo had agreed to the alliance, including factions from the Islamic Front, which was a merger of rebel groups announced last year.
The Turkish prime minister Davutoglu accuses Syrian forces of committing massacres in and around Aleppo and worries that this could lead to a major refugee crisis in Turkey