North Korea threatened on Monday to shoot down U.S. military planes, even if they are not in the country's airspace, arguing that President Trump's bellicose tweets amount to a declaration of war.

The remark by Ri Yong Ho, Pyongyang's foreign minister, represented another escalation in tensions stoked by a series of insults and threats hurled between Trump and North Korean leader Kim Jong Un and his regime. Even though Pyongyang's military capability is considered far outmatched by U.S. technology and pilot training, Ri's rhetoric raised anxieties that a simple miscalculation could spark a military confrontation and spiral out of control.

"Fiery talk can lead to fatal misunderstandings," said Stéphane Dujarric, spokesman for U.N. Secretary General António Guterres.

Last week, at the U.N. General Assembly, Ri revealed that his country is considering testing a hydrogen bomb somewhere over the Pacific Ocean. On Monday, he made a more direct threat against the United States, which Pyongyang considers its archenemy, bent on destroying the regime.

"The whole world should clearly remember it was the U.S. who first declared war on our country," said Ri, speaking to reporters in New York in reference to Trump's comments at the General Assembly last week and again Saturday on Twitter.

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

"The question of who won't be around much longer will be answered then," Ri added, responding to Trump's weekend tweet warning that if Ri "echoes thoughts of Little Rocket Man, they won't be around much longer!" Trump has repeatedly used the belittling epithet for Kim Jong Un.

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North Korea's willingness to shoot down U.S. aircraft is not in question. It has done so before, most notably in 1969, during the Nixon administration, when a Navy plane on a reconnaissance mission was downed by North Korean MiGs over the Sea of Japan, or East Sea. All 31 Americans on board were killed. There was no retaliation, and the United States resumed reconnaissance flights off the coast of North Korea a week later.

The United States and North Korea, which have technically remained in a suspended state of war since the 1953 armistice, have had other saber-rattling standoffs.

In 1976, for example, North Korean soldiers axed to death two U.S. service members who ventured into the demilitarized zone separating North and South Korea, leading President Gerald R. Ford to put all U.S. troops in South Korea on the highest level of military readiness.

In 1981, a North Korean ­surface-to-air missile was fired at a U.S. reconnaissance plane flying near the DMZ, but it missed.

It is unknown whether North Korea has the ability to challenge the U.S. Air Force today. Most of its surface-to-air missiles and fighter planes are decades old, many dating to the 1950s and 1960s, when they were acquired from the Soviet Union.

"If there is a war, South Korean and U.S. military pilots will soon become aces as they shoot down North Korean aircraft," said ­David Maxwell, a retired Army Special Forces colonel who served in Korea and now is associate director of the Center for Security Studies at Georgetown University. "The North Korean air force is no match for them."

Even as a threat lacking the might to back it up, however, Ri's comments underscore the urgency behind the growing crisis over North Korea. After many of its 2016 missile launches failed, Pyongyang has in recent months accelerated its testing of ­medium-range and long-range missiles, and has detonated what it claims was a hydrogen bomb. The speed of the North Korean advances surprised even many military analysts.

North Korea is not believed to possess more-advanced surface-to-air missile systems such as the Russian S300s and S400s, unless they were acquired clandestinely.

"It's hard to be sure what they have," said Dean Cheng, an Asia expert with the Heritage Foundation. "They're not necessarily going to parade them through Pyongyang."

Army Col. Robert Manning III, a Pentagon spokesman, said Monday that North Korea's threat to shoot down American warplanes will not change U.S. military operations. U.S. bomber flights conducted this weekend off the Korean Peninsula's east coast occurred in international airspace, where the Pentagon has a right to fly, he said.

The White House rejected Ri's characterization that the two countries are in a state of open war.

"We've not declared war on North Korea," said press secretary Sarah Huckabee Sanders. "And frankly, the suggestion of that is absurd."

Sanders said it is "never appropriate" to shoot down another country's aircraft when flying in international airspace.

"Our goal is still the same," she added. "We continue to seek the peaceful denuclearization of the Korean Peninsula. That's our focus, doing that through both the most maximum economic and diplomatic pressures as possible at this point."

Many experts are concerned that tensions are being inflamed by the warlike rhetoric between North Korea's leadership and Trump, starting with his combative address to the General Assembly last week, in which he said the United States was ready, willing and able to "totally ­destroy" North Korea.

"The United States has great strength and patience, but if it is forced to defend itself or its allies, we will have no choice but to totally destroy North Korea," Trump said.

Since then, the hostile comments have flown back and forth almost daily, with Kim calling Trump a "mentally deranged U.S. dotard" and Trump gleefully repeating the "Little Rocket Man" put-down.

On Saturday, Ri said that Trump's mockery of Kim made it "inevitable" that rockets would "visit" the U.S. mainland, while North Korea released doctored videos showing North Korean missiles shooting down U.S. planes and scoring a direct hit on an aircraft carrier.

Many experts dismiss the North Korean threats, at least for now.

"They do an excellent job of trying to deter by bluster," said Bruce Bennett, a North Korea expert with the Rand Corp., a research organization. "They've been very successful convincing a lot of people it's too dangerous to take them on when they're such a weak country militarily in many ways."

But with the chances for a military confrontation growing, North Korea is proving it cannot be dismissed for long.

"We should absolutely take them seriously," said Cheng of the Heritage Foundation. "North Korea has demonstrated its willingness to use force against South Korean sailors, soldiers and civilians. So it's very difficult to predict what it would or would not do."

Dan Lamothe and John Wagner contributed to this report.

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