Video released by Syrian Civil Defense Forces shows aftermath of alleged Russian air strikes.
Approximately 300 workers have been missing since Monday.
Jaish al-Islam says it's still coming under attack from government forces.
Syrian President Bashar al-Assad has meanwhile told refugees to come home.
Assad's government says Turkish military action in northern Syria supports "armed terrorist organizations."
The band has also written a song for Paris following the November 13 attacks.
Rape for "honor crimes" is deeply ingrained and widespread in Syria's Islamic society.
Only 14 percent of Russians support their military's involvement in Syria.
"The city is now totally controlled by gunmen and its destiny is dark and dim."
Eyewitness details helicopter strike on camp's biggest hospital as joint military operation is announced.
Assad pledges to beat back extremists by arming refugees after two-year siege.
In a separate advance, rebel groups that have received backing from Assad's Arab and Western foes captured a border crossing with Jordan.
Socialist chairman denounces Assad as 'a butcher' after French cross-party delegation visits Damascus this week.
The lawyers, who documented abuses in Syria, are being held by opposing sides in the country's ongoing conflict.
New campaign argues that illicit trade is turning Syrian history into a weapon of war