Trump warns Assad regime of big price after attack in Syria

US President Donald Trump today warned Syrian President Bashar al-Assad that there would be a "big price to pay" for a chemical attack against a violence-hit town in Syria where dozens of Syrians choked to death.

Trump also called Assad an "animal" and blamed Russia and Iran for backing him.

"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," Trump said in a series of tweets on Sunday.

"President Putin, Russia and Iran are responsible for backing Animal Assad. Big price to pay," Trump said, warning his Russian counterpart Vladimir Putin and Iran for backing the authoritarian Assad regime.

Trump aso accused former President Barack Obama for the Syrian disaster, saying if his predecessor's actions could have stopped "Animal Assad" long ago.

"If President Obama had crossed his stated Red Line In The Sand, the Syrian disaster would have ended long ago! Animal Assad would have been history!" Trump said in another tweet.

At least 80 civilians have been killed since yesterday after the regime launched fresh air raids on rebel-held areas of Eastern Ghouta, according to the Syrian Observatory for Human Rights, a Britain-based monitor.

Syrian state media and the regimes ally Russia denounced claims of chemical use as "fabrications".

Tom Bossert, the White House Homeland Security Advisor, ruled out taking out any policy option, ABC News reported.

"I wouldn't take anything off the table," he said responding to a question if there would be another missile attack.

"These are horrible photos. We're looking into the attack at this point. The State Department put out a statement last night and the president's senior national security cabinet have been talking with him and with each other all throughout the evening and this morning, and myself included," Bossert said.

Trump, he said, has got a point that's been very clear.

"The pendulum has swung in the wrong direction for too long and the United States of America has been take advantage of in their responsibility to provide security for the entire world," he said.

"It is time to move that pendulum back in a way that brings regional partners and others with equities in these matters all around the globe into putting their resources and their treasure and their boys and girls on the line, and not just American troops," Bossert added.

Top American Senator Lindesay Graham said that the Syrian chemical attack is a defining moment for Trump.

"It is a defining moment in his presidency, because he has challenged Assad in the past not to use chemical weapons. We had a one-and-done missile attack. So Assad is at it again. They see us, our resolve, breaking. They see our determination to stay in Syria waning. And it's no accident they used chemical weapons," Graham told ABC News.

"But President Trump can reset the table here. To me, I would destroy Assad's air force. I would create safe zones in Syria where people can come back to their country from the surrounding area and live a better life. Train up Syrians to take on Assad so we can negotiate in Geneva from a position of strength," he said.