Not all US lawmakers have welcomed the "illegal" strike on Syria ordered by President Donald Trump that was allegedly in retaliation for a staged chemical attack in the suburb of Damascus last week.

Without having the mandate from the United Nations, Washington and two of its European allies have launched strikes against Syrian targets, seeking to retaliate against President Bashar Assad for a suspected chemical attack near Damascus on April 7, which, according to unconfirmed reports, killed dozens of people.

"We are prepared to sustain this response until the Syrian regime stops its use of prohibited chemical agents," Trump said in a televised speech on Friday evening, accusing Assad of carrying out "crimes of a monster."

The US actions on foreign soil were taken by the president without the direct approval of lawmakers on Capitol Hill. Following Trump's announcement, a number of them have condemned the move.

"This military action against Syria is a strike against a foreign government. Such an act requires a Congressional authorization to use force, and we have not provided one," Rep. John Garamendi (D-California) said on Twitter.

"By illegally bombing Syria, President Trump has once again denied the American people any oversight or accountability in this endless war. Congress, not the president, has the power to authorize military action," Rep. Barbara Lee (D-California) tweeted after Trump ordered the strike.

The strike was also called "illegal" by Senator Tim Kaine (D-Virginia), who noted that Trump does not have any legal authority to wage war against nation states. He wondered if Iran and North Korea will also witness the wrath of the US soon.

The same sentiment was voiced by Senator Jeff Merkley (D-Oregon), who urged Trump to have a clear exit strategy prior to involving US troops abroad.

"I haven't read France's or Britain's 'Constitution,' but I've read ours and no where in it is Presidential authority to strike Syria," Rep. Thomas Massie (R-Kentucky) added.

The American military response abroad "must come through congressional approval," Rep. Lucille Roybal-Allard (D-California) said on Twitter. ‏"Instead, President Trump has once again struck Syria on his own."