Russia's defense ministry said it had lost contact with an IL-20 aircraft with 14 servicemen on board near Syria's Hmeimim airbase, Syrian state-run Ikhbariya TV reported late on Monday.

Amid the destruction, which has left more than 140,000 dead, presidential elections may seem impossible. Syrian officials insist they will be held on time.

An initial plan to destroy chemicals and weapons in a third country was rejected after no nation was willing to accept the hazardous waste.