Eric Trump says he is "sure" his sister Ivanka used her influence over their father to encourage the US president to launch military action against Bashar al-Assad in Syria.

Donald Trump ordered air strikes against a Syrian air base last Thursday night in response to a chemical weapons attack by the Assad regime on April 4 which killed at least 87 people, including more than 30 children.

“Ivanka is a mother of three kids and she has influence. I’m sure she said: ‘Listen, this is horrible stuff,’" Eric Trump told the Telegraph.

“My father will act in times like that. And by the way, he was anti doing anything with Syria two years ago. Then a leader gasses their own people, women and children. At some point America is the global leader and the world’s superpower has to come forward and act and they did with a lot of support of our allies and I think that’s a great thing.”