RUSSIAN HELICOPTER SHOT DOWN

The helicopter came down in Idlib province, roughly mid-way between Aleppo and Russia's main air base at Khmeimim in the western province of Latakia, near the Mediterranean coast.

Russian air power began supporting Syrian President Bashar al Assad late last year, an intervention which tipped the balance of the war in Assad's favor, eroding gains the rebels had made that year.

The Russian defense ministry said the Mi-8 military transport helicopter was shot down after delivering humanitarian aid to Aleppo as it made its way back to Khmeimim.

No group has claimed responsibility for downing the helicopter.

the Helicopter that was shot down

Government and opposition forces have both denied using chemical weapons during the five-year-old civil war. Western powers say the government has been responsible for chlorine and other chemical attacks. The government and Russia have accused rebels of using poison gas.

U.N. investigators established that sarin gas was used in Eastern Ghouta in 2013. The United States accused Damascus of that attack, which it estimates killed 1,429 people, including at least 426 children. Damascus denied responsibility, and blamed rebels.

Later that year the United Nations and the Syrian government agreed to destroy the state's declared stockpile of chemical weapons, a process completed in January 2016.

The Organisation for the Prohibition of Chemical Weapons confirmed in late 2015 that sulfur mustard, commonly known as mustard gas, had been used for the first time in the conflict, without saying which party in the many sided conflict it thought had used it.

(Editing by Samia Nakhoul and Robin Pomeroy)