In a briefing to reporters outside the U.N. Millennium Plaza Hotel in New York City on Monday, North Korea’s Foreign Minister Ri Yong-ho threatened to shoot down U.S. strategic bombers even when they are flying outside of North Korean airspace.

“The whole world should clearly remember it was the U.S. who first declared war on our country,” said Ri. “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.”

Ri’s comments were part of a steadily escalating rhetorical volley that began with President Trump’s address to the U.N. General Assembly, in which he memorably sneered at North Korean dictator Kim Jong-un as “Rocket Man” and said he was on a “suicide mission for himself and his regime.”

“The U.S. 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 last Tuesday at the United Nations.

On Saturday, U.S. bombers flew close to the North Korean coast in a show of force that took them further north than any American fighter or bomber has flown during the 21st century, according to the Pentagon.

North Korea has long complained about U.S. bomber flights near the Korean peninsula; it’s one of the reasons they occasionally threaten to attack Guam, where American B-1B bombers are based. The North Koreans have demanded an end to joint U.S.-South Korean military drills as a precondition for any further negotiations about their nuclear missile program, which they refuse to halt in any event.

On Saturday, Foreign Minister Ri Yong-ho parodied Trump’s “insults” against Kim Jong-un by telling the United Nations that “none other than Trump himself is on a suicide mission.”

“In case innocent lives of the US are harmed because of this suicide attack, Trump will be held totally responsible,” said Ri. He also called President Trump a “mentally deranged person full of megalomania,” who holds the American “nuclear button” in his remarks.

“The dangerous reality is that the gambler who grew old using threats, frauds, and all other schemes to acquire a patch of land holds the nuclear button. This is what constitutes the gravest threat to international peace and security today,” the foreign minister declared.

Trump, as is his custom, responded to Ri’s speech with a tweet:

In his comments Monday, Ri repeatedly referred to Trump’s comments as equivalent to a declaration of war against North Korea. He claimed North Korea’s nuclear missile program is “to all intents and purposes, a war deterrent for putting an end to nuclear threat of the US and for preventing its military invasion, and our ultimate goal is to establish the balance of power with the U.S.”

He added that Trump’s “Rocket Man” insult makes their “rocket’s visit to the entire U.S. mainland inevitable all the more.”