Trump said US forces launched "precision" strikes against Syrian targets, and that the United States would "sustain this response until the Syrian regime stops its use of prohibited chemical agents."

House Minority Leader Nancy Pelosi led calls for Trump to map out a detailed plan and present it to Congress if he wants to expand military action.

"One night of air strikes is no substitute for a coherent strategy," Pelosi said in a statement.

Trump "must come to Congress to obtain a new AUMF (authorization for use of military force), present a clear set of objectives, & ultimately hold Putin accountable for the bloodshed he has enabled," she added, referring to President Vladimir Putin of Russia, the Syrian regime's most powerful ally.

US military forces have largely been operating under AUMFs passed by Congress shortly after the 9/11 attacks to conduct operations against extremist groups like the Islamic State, including in Syria.

Some Democrats like Senator Tim Kaine, the party's vice presidential nominee in 2016, said although last week's deadly apparent chemical attack was an abomination, Trump's air strikes were illegal.

"The last thing Congress should be doing is giving this president a blank check to wage war against anyone, anywhere. We need to put clear limits in place before he starts another war," said Kaine.

"Today, it's a strike on Syria - what's going to stop him from bombing Iran or North Korea next?"

Congressman Eric Swalwell reminded that Trump launched missile strikes without congressional approval against a Syrian air field last year.

"What's changed? Zero. They're still using chemical weapons," he said. "This is the result of a failure to have a strategy and engage Middle East countries to solve this problem."

Republican lawmakers largely backed the assault.

"The precision targeting of military targets are needed in the fight of good versus evil, a fight of the United States versus the dark edge of humanity," Senator Cory Gardner said.

But some libertarian Republicans, notably congressman Justin Amash, expressed full-throated opposition.

"These offensive strikes against Syria are unconstitutional, illegal, and reckless," Amash said, adding that the next House speaker who succeeds outgoing Paul Ryan should "reclaim congressional war powers."