North Korea’s foreign minister said Monday that the U.S. had “declared war” on the isolated nation, pinning the blame on President Donald Trump’s incendiary words days earlier while also threatening to shoot down U.S. bombers — even if they are not in the country’s airspace.

The White House later in the day dismissed the claim as “absurd,” but observers said the risk of miscalculation between the two nuclear-armed nations had hit a level unseen in recent years.

“The whole world should clearly remember it was the U.S. who first declared war on our country,” North Korean Foreign Minister Ri Yong Ho said during a televised news conference in New York.

“Since the United States declared war on our country, we will have every right to make countermeasures, including the right to shoot down the United States strategic bombers even when they are not yet inside the airspace border of our country,” he added.

“The question of who won’t be around much longer will be answered then,” Ri said in reference to a cryptic Twitter post by Trump on Saturday.

Ri’s comments came in the wake of a war of words between North Korean leader Kim Jong Un and Trump that saw the U.S. president — in a speech before the U.N. General Assembly last week — vow to “totally destroy” the country of 25 million people if the United States is forced to defend itself or its allies.

Trump also used the speech to take a jab at Kim, deriding him as a “rocket man … on a suicide mission,” words that hit a nerve in the North, where the young leader is regarded as an almost godlike figure.

Kim said he would make the U.S. “pay dearly” for threatening his country’s destruction, and that he was considering the “highest level of hard-line countermeasure in history” — a statement Ri later hinted could mean a detonation of a powerful hydrogen bomb over the Pacific Ocean.

On Saturday, Trump had appeared to condone the assassinations of both Ri and Kim in his tweet after the foreign minister unleashed a fiery speech before the General Assembly earlier the same day.

“Just heard Foreign Minister of North Korea speak at U.N. If he echoes thoughts of Little Rocket Man, they won’t be around much longer!” he wrote.

Later Monday, answering a question about whether Trump’s tweet had amounted to a declaration of war, White House press secretary Sarah Huckabee Sanders poured cold water on Ri’s claim.

“We’ve not declared war on North Korea,” she told a news conference. “And frankly, the suggestion of that is absurd.”

While the U.S. has said that “all options are on the table” — including military action — for dealing with the North Korean crisis, the White House has also maintained that diplomacy is the preferred route.

Trump, however, has taken a harder-line stance than many of his predecessors, relying more on heated words and military muscle-flexing which has included joint U.S.-Japan exercises over Japanese airspace and flights near the two Koreas’ border by U.S. bombers and South Korean fighter jets.

On Saturday, U.S. B-1B heavy bombers from Guam and F-15C fighter escorts from Okinawa flew in international airspace to the farthest point north of the two Koreas’ border that any such American aircraft had gone this century.

That operation was the latest in a series of recent flights near the tense border that the North has lambasted as rehearsals for invasion and strikes on its leadership.

South Korea’s spy agency said Tuesday that the flight, which it said occurred north of the Northern Limit Line (the de facto maritime boundary between the two Koreas), had prompted Pyongyang to bolster its defenses on its eastern coast, the Yonhap news agency reported.

The unverified Yonhap report suggested that the flight had taken the North by surprise or that it had intentionally avoided any response since the flight had been conducted in international airspace.

Speaking at a forum in Washington, U.S. national security adviser H.R. McMaster said the Trump administration had come up with “four to five” scenarios in which the North Korean nuclear and missile threat is resolved.

“Some are uglier than others,” he said, according to video of a speech hosted by the Institute for the Study of War.

“What we hope to do is avoid war, but we cannot discount that possibility,” McMaster added.

Although McMaster said there is “not a military blockade that can solve the problem,” the South Korea’s Defense Ministry said last week that its military would conduct a joint drill involving a U.S. aircraft carrier — likely the Yokosuka, Kanagawa Prefecture-based USS Ronald Reagan — next month.

A report Tuesday by the South’s Chosun Ilbo daily citing unidentified government sources said the U.S. was considering sending an aircraft carrier group “into North Korean waters” or deploying B-2 stealth bombers and F-22 stealth fighters to the Korean Peninsula.

Ri, who was wrapping up his visit to the U.N. General Assembly on Monday, said at the end of his news conference that Pyongyang, too, would not rule any options out.

“In light of the declaration of war by Trump, all options will be on the operations table of the supreme leadership of the DPRK,” he said, using the acronym for the North’s formal name, the Democratic People’s Republic of Korea.

But the North’s military capabilities, including its ability to down sophisticated U.S. warplanes, are limited. Despite diverting significant sums of cash into its armed forces, its air force is said to be undertrained and outdated, while numerous rounds of international sanctions have reportedly left it thirsty for fuel.

Still, the searing rhetoric by Ri and Trump highlights growing fears that U.S. and North Korea could inadvertently stumble into conflict.

Experts said the odds of such a misreading of intentions has been steadily increasing amid the ramped-up military operations in the region, and the heated and sometimes personally insulting exchanges between Trump, Kim and others.

“The risk of miscalculation goes up when military forces are operating more assertively and frequently and this is accompanied by an escalation of rhetoric about the willingness to go to war,” said Sheila Smith, a senior fellow for Japan studies at the Council on Foreign Relations. “Clearly, we have been in an escalatory spiral with Pyongyang since earlier this year.”

Smith said that while the U.S. may be acclimatized to Pyongyang’s frantic rhetoric, Washington and its allies “are far less comfortable with the U.S. escalating the rhetoric about going to war.”

“The question is whether either side believes — and is preparing for — doing what it says they are going to do,” she said.

In his speech before the General Assembly on Saturday, Ri used that platform to blast Trump, calling him “a mentally deranged person full of megalomania and complacency” with his finger on the “nuclear button.”

Ri also vowed that his country would take “merciless pre-emptive action” if it detects U.S. or allied military action against it.

“We will take preventive measures by merciless pre-emptive action in case the U.S. and its vassal forces show any sign of conducting a kind of ‘decapitating’ operation on our headquarters or military attack against our country,” Ri said, referring to strikes against the North Korean leadership.

“However, we do not have any intention at all to use or threaten to use nuclear weapons against the countries that do not join in the U.S. military actions against the DPRK,” he added.

The United States and South Korea are technically still at war with the North because the 1950-53 Korean conflict ended in an armistice and not a peace treaty.

Since the armistice, the North has engaged U.S. aircraft numerous times in the skies, though the most well-known — and deadliest — of these incidents was the 1969 shootdown of an American reconnaissance plane over the Sea of Japan that killed all on board. The 31 deaths were one of the biggest single losses of U.S. military lives during the Cold War.

While Washington has said it is not seeking regime change, Pyongyang remains deeply suspicious of U.S. intentions after the ouster and killing of Saddam Hussein in Iraq and Moammar Gadhafi in Libya, both of whom gave up fledgling nuclear programs.

If the North were to identify a legitimate U.S. attempt to strike the regime, or misread a flight such as Saturday’s as such, “it would fit with North Korean practice to strike first — at a ship or plane, perhaps — as an offensive type of deterrence,” said James Schoff, an East Asia expert with the Carnegie Endowment for International Peace in Washington.”

The North has attacked South Korean forces, sinking a warship and killing 46 sailors in 2010. It has also, at times, lashed out at the U.S. military, shooting down and killing one of the pilots of an army helicopter in 1994 after it strayed into North Korean airspace.

Schoff said the Kim regime could then use Ri’s declaration of war statement to justify going on the offensive.

Despite strict U.N. sanctions, and China’s announcement Saturday that it will limit energy supplies to the North and stop buying its textiles under new U.N. measures, the North has maintained that its nuclear and missile programs are crucial to the Kim regime’s survival and has ruled out denuclearization, calling its atomic arsenal a “war deterrent.”

The country conducted its sixth and largest nuclear test — purportedly of a thermonuclear, or hydrogen, bomb — on Sept. 3, and has launched dozens of missiles this year as it moves closer to mastering the technology needed to reliably target the United States with a nuclear-tipped missile.

In July, it conducted two tests of an intercontinental ballistic missile (ICBM) that experts say is capable of striking a large chunk of the U.S., and on Sept. 15 it lobbed an intermediate-range missile over Japan and into the Pacific Ocean for the second time.