"We are studying that situation extremely closely.  We are meeting with our military and everybody else, and we’ll be making some major decisions over the next 24 to 48 hours," Trump told reporters.

"We are very concerned when a thing like that can happen.  This is about humanity.  We’re talking about humanity.  And it can’t be allowed to happen," he said.

He said: "So if it’s Russia, if it’s Syria, if it’s Iran, if it’s all of them together, we’ll figure it out and we’ll know the answers quite soon.  So we’re looking at that very, very strongly and very seriously."

Russia has invited for a fair investigation into the alleged Syrian chemical attack incident.

Russian Foreign Minister Sergey Lavrov was quoted as saying by TASS: " We are in total support of a fair and immediate investigation, when they ask for it. However, when the investigation is intended to come at a predetermined point - that is, it was done by Assad with Putin’s support - there are no grounds for a serious discussion."

US President Donald Trump earlier attacked Russian President Vladimir Putin and Syrian President Bashar al-Assad over the suspected chemical attack.

Trump tweeted: "Many dead, including women and children, in mindless CHEMICAL attack in Syria. Area of atrocity is in lockdown and encircled by Syrian Army, making it completely inaccessible to outside world. President Putin, Russia and Iran are responsible for backing Animal Assad. Big price. To pay. Open area immediately for medical help and verification. Another humanitarian disaster for no reason whatsoever. SICK!."

The White House issued a statement where it said that Trump spoke to President Emmanuel Macron of France and both the leaders condemned the attack.

The statement said both the leaders agreed that the Assad regime must be held accountable.

"Both leaders strongly condemned the horrific chemical weapons attacks in Syria and agreed that the Assad regime must be held accountable for its continued human rights abuses.  They agreed to exchange information on the nature of the attacks and coordinate a strong, joint response," read the statement issued by the White House.

Moscow said that there will be dire consequences if the West uses this as an excuse to attack Syria.

A chemical attack in Douma, the last rebel-held stronghold near Syria's capital, Damascus, has killed at least 70 people and affected hundreds, rescue workers have told Al Jazeera.