US President Donald Trump has triggered a fresh wave of outrage and condemnation after accusing opponents — who did not applaud during his first State of the Union address — of "treason".

Speaking at a manufacturing plant in Cincinnati, Ohio, on Monday (5 February), the Republican leader criticised Democratic lawmakers who failed to stand and applaud as he listed his achievements before Congress last Tuesday.

While Trump spoke about immigration, infrastructure and economic gains during his first year in office, many Democrats in the audience remained seated and avoided clapping. In some cases, their unimpressed reactions made waves on social media. Trump reportedly called their reaction "un-American" and "treasonous".

"It was a game, you know it's a game. They play games," Trump pointed out, referring to his opponents. "They were told don't even make a facial movement... Dead silence. Not a smile."

He added that the Democrats "would rather see Trump do badly than our country do well".

"It's very selfish," he continued. "It got to a point where I really didn't even want to look too much during the speech over to that side, because honestly it was bad energy."

While Republicans applauded throughout his speech as he listed historically low levels of unemployment among African-Americans and Hispanics, Trump said the Democrats remained silent despite the "positive news".

"You're up there, you've got half the room going totally crazy wild, they loved everything, they want to do something great for our country," Trump said. "And you have the other side... they were like death and un-American. Somebody said treasonous. I mean, yeah, I guess, why not. Can we call that treason? Why not? I mean they certainly din't seem to love our country very much."

Treason is a capital offense in the USand is punishable by death.

Many Democratic lawmakers and irked social media users immediately fired back at the president for his latest "outrageous" remark saying "we don't live in a dictatorship or a mornarchy".

Representative Don Beyer of Virginia tweeted: "@realDonaldTrump doesn't know what "treason" means. He should study Article III of the United States Constitution, which he clearly hasn't read. The Founders were concerned that a despot might abuse their powers of office to attack political enemies. Smart people, the Founders."

Even the official Twitter feed for Dictionary.com and Merriam-Webster got in on the action and tweeted the definition of the word "treason".

"We don't live in a dictatorship or a monarchy," Senator Tammy Duckworth wrote. "I swore an oath—in the military and in the Senate—to preserve, protect and defend the Constitution of the United States, not to mindlessly cater to the whims of Cadet Bone Spurs and clap when he demands I clap."

"What will it take for the Republicans to actually stand up to this madness?" One person asked.