Washington: President Donald Trump is condemning what he calls a "mindless CHEMICAL attack" in Syria that has killed women and children, though he's offering 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.

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

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

Trump is calling for the area to be opened "immediately for medical help and verification. Another humanitarian disaster for no reason whatsoever. SICK!".