Some US lawmakers have begun suggesting that President Donald Trump should respond militarily to the chemical attack in Syria on Saturday.

Sen. Susan Collins said Trump should consider a "targeted attack" like the one he authorized last year, and Sen. Mike Rounds said he needs to "send a message once again that what he said he meant."

Trump tweeted that "President Putin, Russia and Iran are responsible for backing Animal Assad. Big price ... to pay."

Some US lawmakers have begun suggesting that President Donald Trump should respond militarily to the suspected chemical attack in Syria on Saturday.

At least 40 people were killed and hundreds more were injured in Douma, a suburb of Damascus that's the last rebel-held city in the Eastern Ghouta area. Estimates of the death toll from what appeared to be poison gas range up to 150.

"Last time this happened, the president did a targeted attack to take out some of the facilities. That may be an option that we should consider now," Sen. Susan Collins said on CNN's "State of the Union."

After the US concluded that President Bashar al-Assad's regime was behind the April 2017 chemical attack in Khan Sheikhoun, Trump ordered a strike of 59 Tomahawk cruise missiles on Shayrat airfield and nearby military infrastructure controlled by Assad.

Sen. Mike Rounds of South Dakota said on NBC's "Meet the Press" that Trump needs to "send a message once again that what he said he meant" and "act decisively" once he knows what his options are.

"That's appropriate. It was appropriate a year ago. It would be appropriate today," Rounds said, referring to the 2017 strike. "I think we wait until the Secretary of Defense puts together his proposals, [and] he lays them in front of the president."

In this image from video provided by the U.S. Navy, the guided-missile destroyer USS Porter (DDG 78) launches a tomahawk land attack missile in the Mediterranean Sea, Friday, April 7, 2017. Mass Communication Specialist 3rd Class Ford Williams/U.S. Navy via AP

Putting pressure on Putin

Lawmakers also encouraged the president to put more pressure on Russian President Vladimir Putin, whose government and military have backed Assad.

"It is further reason why it is so important that the president ramp up the pressure and the sanctions on the Russian government, because, without the support of Russia, I do not believe that Assad would still be in office," Collins said.

House Speaker Paul Ryan said the attack "is a horror that cannot be tolerated by responsible nations." "The U.S. must continue to lead an international effort to hold the Assad regime and Russia accountable for their actions," the Wisconsin representative tweeted on Sunday.

The Pentagon did not immediately respond to Business Insider's request for comment on the possibility of another US strike.

Trump tweeted on Sunday that "President Putin, Russia and Iran are responsible for backing Animal Assad. Big price ... to pay."

Russia said on Sunday that military "intervention under false & fabricated pretexts in Syria, where Russian servicemen stay at the request of the legitimate government, is absolutely unacceptable and may trigger the gravest consequences," according to Washington Post Beirut bureau chief, Liz Sly.

"We cannot avert our eyes," Sen. Richard Blumenthal of Connecticut tweeted on Sunday. "Time to confront this horrific crisis with action ... Time for real leadership from Trump. More than merely words, action is necessary to hold Russia, as well as Syria & Iran, accountable."