President Donald Trump is pressing for an aggressive U.S. strike against Syria.
Military chiefs have recommended that he tone down his position.
A senior official said Trump has asked his military to consider options to punish Russia and Iran.
Russia and Iran are major supports of Syria.
Defense Secretary Jim Mattis has warned that an attack creates risk of a confrontation with Russia.
“President Putin, Russia and Iran are responsible for backing Animal Assad.” President Donald Trump via Twitter
