Obama has special forces in Turkey and Jordan aiding Syrian rebels.
Russia has special forces supporting Assad, possibly manning anti-aircraft sites.
Days ago, Obama claims Assad my be using chemical weapons...crossing the line.
Days later, Putin claims Syrian rebels took a pot shot at a Russian civilian airliner...crossing the line.
Just tit-for-tat.
update today:
Five people were killed in an explosion April 30 at Marjeh Square in central Damascus, a monitoring group said, Reuters reported. A pro-government television channel showed widespread damage.