U.S. President Donald Trump hailed a bustling economy in his first State of the Union speech on Tuesday in which he also laid out his immigration reform proposal, expressing hope that it would win support from opposition Democrats.

Trump took credit for economic growth in the first year of his presidency as well as low unemployment and rising wages, telling members of Congress and the nation that business confidence is at an all-time high.

He touted tax cuts passed in December, reduced federal regulations, bonuses paid to workers and corporations that have announced planned investment, saying all these things have further stoked growth.

He also announced that he had signed an order reversing his predecessor Barack Obama's not-yet-fulfilled directive to close the military prison at Guantanamo Bay, Cuba.

The president said he was asking Congress to ensure that the US continued to have the power to detain terrorists and ensure that the U.S. military did not "meet them again on the battlefield."

In his State of the Union address to Congress and the nation, Trump also described Moscow and Beijing as challenging "our interests, our economy, and our values." But he saved his harshest words for Iran and North Korea.

"North Korea's reckless pursuit of nuclear missiles could very soon threaten our homeland," he warned, implying he has a narrow window to respond to Pyongyang's ambition.

"We are waging a campaign of maximum pressure to prevent that from ever happening."

Singling out Iran and North Korea -- which along with Iraq formed his predecessor George W. Bush's "Axis of Evil" -- seemed calculated to raise the specter of new conflicts.

It came as a respected Korea expert, tipped to become Trump's ambassador to Seoul, revealed he had dropped out of the running and criticized the idea of a pre-emptive strike.

Secretary of State Rex Tillerson and Defense Secretary Jim Mattis have been pushing a diplomatic strategy to convince North Korean leader Kim Jong-Un to come to the table and negotiate away his nuclear arms.

But other senior figures have reportedly endorsed the idea of a "bloody nose" strike to damage Kim's nuclear sector and show the U.S. means business, hopefully without provoking a wider war.

Victor Cha, a senior adviser at the Center for Strategic and International studies and until Tuesday a candidate for U.S. ambassador to Seoul, rejected this in the Washington Post.

"A strike (even a large one) would only delay North Korea's missile-building and nuclear programs, which are buried in deep, unknown places impenetrable to bunker-busting bombs," he wrote.

Complacency and concessions

"A strike also would not stem the threat of proliferation but rather exacerbate it," he added, warning that Kim might try to sell nuclear weapons to "bad actors" for money or revenge.

Cha also pointed out that millions of South Koreans and tens of thousands of American expats and troops would be at immediate risk of a North Korean counterstrike.

"The president would be putting at risk an American population the size of a medium-size U.S. city... on the assumption that a crazy and undeterrable dictator will be rationally cowed by a demonstration of U.S. kinetic power," Cha wrote.

According to the Post, Cha's refusal to entertain the idea of a pre-emptive strike cost him his ambassadorship, and Trump's speech suggested he was in no mood for compromise.

"Past experience has taught us that complacency and concessions only invite aggression and provocation," he declared.

"We need only look at the depraved character of the North Korean regime to understand the nature of the nuclear threat it could pose to America and to our allies."

Trump also upped the ante in his stand-off with Iran, vowing U.S. support for street protests against Tehran's clerical regime.

And again he compared himself favorably to his predecessor Barack Obama, suggesting that it had been a mistake not to back the failed 2009 Green Revolution in Iran.

"When the people of Iran rose up against the crimes of their corrupt dictatorship, I did not stay silent," he declared.

"America stands with the people of Iran in their courageous struggle for freedom," he promised, to applause from assembled lawmakers.

The president also highlighted gains made against the Daesh terror group in Iraq and Syria, while warning that "there is much more work to be done" in the war against terrorists.