The United States says it believes Russia is responsible for the air strike in Syria. A security adviser also says the US will determine weather the truce can continue.

"All of our information indicates clearly that this was an air strike. That means there only could have been two entities responsible either the Syrian regime or the Russian government," said Ben Rhodes, White House Deputy National Security adviser.

"In any event we hold the Russian government responsible for air strikes in this space given that their commitment under the cessation of hostilities was to certainly ground air operations in places where humanitarian assistance is flowing."