WASHINGTON – President Donald Trump faced immediate blowback on Friday for his assertion that his predecessor in the Oval Office, Barack Obama, was on the brink of starting "a big war" with North Korea.

Trump made the claim during a rambling news conference on Friday, in which he declared a national emergency to free up federal money for his controversial border wall, suggested he would delay a deadline for hiking tariffs on China, and touted his success in negotiations with North Korea.

Trump said Obama told him North Korea's nuclear weapons program presented the greatest threat to the United States during a 2016 meeting in the White House just after Trump won the presidential election.

"He told me he was so close to starting a big war with North Korea," Trump recounted.

"It is absolutely ridiculous to suggest that the Obama administration was considering anything like that," said Michael Fuchs, who served as Obama's deputy assistant secretary of State for East Asian and Pacific affairs. He said Trump was simply "lying" about that exchange.

Other top Obama advisers also sharply refuted Trump's claim.

"We were not on the brink of war with North Korea in 2016," Ben Rhodes, a former national security adviser to Obama, tweeted on Friday. Rhodes suggested that Trump didn't understand Obama's 2016 description of the threat North Korea posed.

John Brennan, Obama's former CIA director, said that while he was not in the room during that meeting, "President Obama was never on the verge of starting any war with North Korea, large or small." Obama viewed North Korea's pursuit of nuclear weapons with "deep concern, and he constantly pressed his national security team to present options to reduce the threat from North Korea," but war was not among those options, Brennan told NBC News.

Experts say any military strike against North Korea would almost certainly result in massive loss of life in South Korea and is far too risky to contemplate. Fuchs said such a move would not only result in "mass casualties" for the South Koreans, but it could "easily spiral" into a greater regional conflict involving the use of nuclear weapons.

"The list of disasters that could be created by a conflict with North Korea are ... too unthinkable to consider," Fuchs said.

He and other experts argue that it was Trump who ratcheted up the danger of a military confrontation with North Korea when he took office in 2017, threatening Kim Jong Un's regime with "fire and fury," among other provocative statements and actions. Now, critics said, Trump is trying to claim credit for progress in negotiations aimed at pressing Kim's regime to relinquish his nuclear arsenal.

"This is again the president, when it comes to North Korea, attempting to play the role of both arsonist and firefighter – acting like there was some big emergency that he saved everyone from," Fuchs told USA TODAY.

Trump is scheduled to hold a second summit with the North Korean dictator later this month in Vietnam. The two men held a high-profile summit last year in Singapore, where they signed a vaguely worded agreement in which North Korea promised to work toward a “complete denuclearization of the Korean Peninsula.”

On Friday, Trump argued the talks with North Korea have resulted in significant progress, noting that Kim's regime has stopped testing missiles and has returned American hostages, among other steps.

But the North Koreans have not taken any visible, concrete steps toward fulfilling that pledge, and Trump's own advisers acknowledge that North Korea is still developing a nuclear weapons program. Trump's top intelligence chief recently warned that North Korea was "unlikely" to ever give up its nuclear weapons.

Trump also addressed his administration's bitter trade negotiations with China, saying he is likely to push back a March 1 deadline for imposing new tariffs on the Asia giant as talks continue.

The president has long accused the Chinese of engaging in unfair trade practices, and he slapped steep tariffs on China last year, sparking retaliatory steps by the Chinese and spawning fears of a trade war.

Trump and Chinese President Xi Jinping agreed to a ceasefire in the tariff war last year and began negotiations for a new trade agreement. They set the deadline of March 1, after which new tariffs would go into effect if no agreement is reached.

But Trump said Friday he would "not increase the tariffs" as long as progress is being made.

Contributing: David Jackson