President Donald Trump has condemning what he calls a "mindless chemical attack" in Syria that has killed women and children.

But the president offered no evidence to support the claim by Syrian opposition activists and rescuers that poison gas was used.

Syrian President Bashar Assad's government is denying the allegations of such an attack on a rebel-held town near Damascus, the capital.

President Trump said in a tweet on Sunday that the "area of atrocity is in lockdown and encircled by Syrian Army, making it completely inaccessible to outside world."

He said Russian President Vladimir Putin and Iran - influential Syrian backers - "are responsible for backing Animal Assad".

President Trump is calling for the area to be opened "immediately for medical help and verification.

Another humanitarian disaster for no reason whatsoever. Sick!"

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