RUSSIA IS OPTING A NUCLEAR STRIKE ON ISIS THE KREMLIN IS AWAITING CONSENT FROM ITS ALLIES
Also Russia had consulted with the Syrian government as well as the governments of its allies in the region, who in turned told the Kurds and other allied militias of a possible nuclear strike, warning them to move allied civilians from areas that might be struck by Russia's nuclear weapons.
SITE has reported that a video purportedly made by either ISIS supporters or ISIS themselves that shows the downing of the airliner.
The White House has declined to make a statement about this incident and the Kremlin's use of nuclear weapons. However, the Kremlin says the use of nuclear weapons is justified to protect its citizens and its interests, namely helping to sustain the government of Bashar Al-Assad and keeping the its allies in power in Iraq and Iran, which are considered allies to Russia. Their common interest in destroying ISIS motivates them to work together.
However, the US has stated its fears that deploying nuclear weapons near the region would spur an nuclear arms race in other nations in the region, namely Saudi Arabia and the nations within the Gulf Cooperation Council, a group of Sunni Muslim nations located in the Persian Gulf region, which have aided in the creation of ISIS and continue to support it like the way they supported Iraqi insurgents during the Iraq War (2003-2011).
Both the US and the UN are concerned that the conflict in the region could lead into a wider conflict, possibly a world war.
(multiple intel reports concerning the downing of the Russian civilian airliner in northern Sinai, ISIS' purpoerted claim of responsibility and Russia's official response)