No decision on Syria yet, Trump weighing all options: White House

US President Donald Trump is weighing all options on the table with regard to Syria as he holds the Syrian regime and Russia responsible for the latest chemical weapons attack, the White House said on Thursday, adding that no final decision has been taken yet on the military response.

"It sounds like all options are on the table, and a final decision hasn't been made, but we'll keep you posted once it is," White House Press Secretary Sarah Sanders told reporters at her daily news conference.

Referring to the allegation of a Russian military official that there was an attack but it was staged by the White Helmets brigade component of the rebels in Syria, she said the intelligence provided "certainly paints" a different picture, and the President holds Syria and Russia responsible for the chemical weapons attack.

In the last few days, Trump has blamed the authoritarian Assad regime for the chemical attack that killed dozens of Syrian civilians, including children and women, in the Damascus suburb of Douma.

"We're maintaining that we have a number of options, and all of those options are still on the table. Final decisions haven't been made yet on that front," Sarah Sanders said, adding that the President has not laid out a timetable.

"In a public sense, certainly the President has made some decisions.? He made a decision not to travel to Latin America so that we could focus on this. That was the first step in this process, but we're continuing to look at a number of options," she said.

Russia, she alleged, holds some responsibility in the fact that they had guaranteed that Syria wouldn't use chemical weapons again, which they did. They also hold some responsibility in the fact that they have the six UN resolutions that they vetoed to help protect Assad. Both of those things lie at Russia's feet in terms of responsibility in this process, Sarah Sanders said.

In a statement, Senator Bernie Sanders said Trump has no legal authority for broadening the war in Syria.

"It is Congress, not the President, who determines whether our country goes to war and Congress must not abdicate that responsibility. We have been in Afghanistan for 17 years and Iraq for 15 years. The result has been massive regional instability, terrible loss of life and a cost of trillions of dollars," he said.

"If President Trump believes that expanding the war in Syria will bring stability to the region and protect American interests, he should come to Congress with his ideas," Bernie Sanders.

Senator Edward Markey, a member of the Senate Foreign Relations Committee, criticised Trump's warnings that he intends to conduct military strikes in retaliation against Assad's use of chemical weapons.

"Before President Trump conducts military operations, he must come to Congress for authorisation," he demanded.

"Numerous, large-scale attacks on another country without Congressional authorisation are unconstitutional, and they push the US closer to what could be an interminable, all-out conflict in Syria. And announcing military actions over Twitter is the height of irresponsibility and contradicts the President's own previous commitment never to disclose America's plans publicly," Markey said.

Sarah Sanders said the Trump administration will follow whatever laws and regulations were necessary for any actions that it takes.

"Because we haven't laid out any specific actions that we plan to take, I can't tell you exactly what needs we would have to go to Congress with," she said.

Meanwhile, Senator John Kennedy from Louisiana requested a classified hearing for members of Congress on the chemical weapons attack in Syria.

"The images of children struggling to breathe after the chemical attack are unconscionable. Whoever did this is a human butcher," he said.

"We need answers to fully understand who is responsible for the attack. We can't let this go unanswered. If we do, our friends won't trust us and our enemies won't respect us," Kennedy added.

Congressman Brad Schneider said the reports from Syria of another major chemical weapons attack against civilians, represent yet one more war crime committed by Bashar al-Assad and his regime.

"Assad must be held to account and the world must clearly demonstrate that chemical weapons are unacceptable anytime, anywhere, and in any context," he said.