Donald Trump considered launching a strike three times as big on Syria, potentially including hitting Russian air defence systems, but was dissuaded by James Mattis, his defence secretary.

The Pentagon presented Mr Trump with three options for how to respond to the chemical attack by the Syrian regime in Douma on April 7, the Wall Street Journal reported.

A first, and most cautious, option consisted of a limited strike on Syrian chemical weapons facilities, while a second targeted those plus military command posts.

The third option had the aim of devastating Bashar al-Assad's military forces and could have targeted Syrian-based Russian air defence capabilities as part of that.

Such a strike would have been three times the size of the military action that was eventually launched by the US, UK and France in the early hours of Saturday.