Escalating threats from North Korea’s communist regime are indicators of a future military attack or another nuclear test in the coming days, according to a recent U.S. intelligence assessment.

Intelligence agencies issued the assessment last week warning that threatening rhetoric from Pyongyang in response to large-scale U.S.-South Korean military exercises and new U.N. sanctions had reached the highest level in years.

The unclassified assessment circulated within government states that the intense language suggests North Korea is preparing for a surprise military strike or a demonstration of strategic capability, such as a new long-range missile test or underground nuclear blast, according to U.S. officials familiar with the report.

On Sunday, North Korean state news media warned its missiles could destroy New York City in a thermonuclear attack.

"Our hydrogen bomb is much bigger than the one developed by the Soviet Union," the outlet DPRK Today stated.

"If this H-bomb were to be mounted on an inter-continental ballistic missile and fall on Manhattan in New York City, all the people there would be killed immediately and the city would burn down to ashes," the report said.

Such threatening rhetoric from Pyongyang is typical of the communist regime’s propaganda. However, in the past several weeks the tone and level of threats has been unusually harsh, according to the officials, and that is increasing fears among intelligence analysts that the stepped-up threats are a prelude to military action or nuclear and long-range missile tests.

Official North Korean statements issued March 4 in response to U.N. sanctions said nuclear forces will be bolstered, but gave no specifics. Other references to possible "incidents" on the peninsula were interpreted as North Korea considering military action.

The United Nations imposed new sanctions on North Korea last month for its underground nuclear test and missile tests. The sanctions required all aircraft from North Korea to be inspected and allows North Korean ships to be stopped and searched for illegal goods.

North Korea last conducted a military provocation in August, using mines to severely wound two South Korean soldiers on patrol in the demilitarized zone separating the two countries.

The deadly attack in March 2010 involving a North Korean submarine that torpedoed the South Korean navy patrol boat Cheonan near the sea border with North Korea, killing 46 sailors, was the last major provocation.

That attack was followed in November 2010 by North Korea’s artillery shelling of Yeonpyeong Island, killing four South Koreans and injuring 19.

South Korea took no action in response to the attacks, other than temporarily broadcasting propaganda into North Korea.

Senior Obama administration officials are worried the next military provocation by North Korea will prompt South Korea to drop its past posture of restraint and conduct a major military counterattack against the North that could trigger a new Korean war.

South Korean President Park Geun-hye announced the adoption of a hardline policy toward North Korea following the recent nuclear and missile tests. The new policy included a cutoff of all trade ties with the North.

The current level of North Korean rhetoric against both the United States and South Korea is not unprecedented. But officials said it is the highest seen since 2013 when North Korea issued threats but did not take action in response to the annual U.S.-South Korean exercises known as Key Resolve and Foal Eagle.

An estimated 290,000 South Korean troops and 15,000 U.S. troops are taking part in this year’s war games, which U.S. officials have said include a scenario for how the two allies’ would carry out a military response to the collapse of the Kim regime in Pyongyang.

North Korea’s verbal fusillade this year included denunciations of what Pyongyang called preparations for a preemptive "decapitation" strike against the North Korean leadership.

North Korea has steadily escalated threatening statements over the past several weeks that have included announced plans for nuclear attacks on both South Korea and the United States.

The most worrying statements were authoritative threats attributed to the National Defense Commission, the regime’s most senior organ in charge of military forces, as well as statements directly from North Korean leader Kim Jong-Un.

The commission warned Feb. 23 that North Korea would take military action in response to the South Korean exercises, including strikes on the presidential compound in Seoul and attacks on the United States. It also warned that more nuclear and missile tests were likely and that it could conduct military attacks on ships and shell border regions, as occurred in 2010.

Kim also threatened to turn Washington and Seoul into "flames and ashes" last week, according to North Korean state media.

The 33-year-old dictator said he would order an immediate nuclear attack if the U.S.-South Korean military drills harmed a single tree or blade of grass in North Korea.

"I will issue a prompt order to launch attack with all military strike means," Kim said.

State Department spokesman John Kirby said Wednesday that the U.S. government takes North Korea’s threats seriously.

"We have to," Kirby told reporters. "But nothing's changed about our resolve in terms of, again, acting in concert with the international community to raise the costs on him for this behavior, and inside the alliance to continue to stand by our South Korean allies in defense of the peninsula."

The Pentagon’s most recent report to Congress on North Korea warned that the Kim regime remains a major threat to the region.

With the world’s fourth-largest military in the world, North Korea could strike with little or no warning, despite shortages of goods and aging equipment, the report said.

"North Korea’s special operations forces, growing artillery, and missile forces provide significant capabilities for small-scale attacks that could rapidly escalate into a larger scale confrontation," the report said.

North Korea is believed to have between 10 and 20 nuclear weapons, although details of the arsenal are not known.

Its missiles include 620-mile-range Nodongs and intercontinental-range Taepodong-2 missiles that the Pentagon says are disguised as space launchers.

North Korea also is developing intermediate-range missiles and submarine-launched ballistic missiles.

Army Gen. Curtis Scaparrotti, the outgoing commander of U.S. Forces Korea, said in a prepared statement to the Senate recently that North Korea is building up nuclear, missile, and cyber forces for its plan of re-unifying the peninsula under its control.

"Similar to his father and grandfather, Kim has likewise demonstrated that violent provocations remain central to North Korea’s strategy," Scaparrotti said Feb. 23.

The most recent example was the North Korean land mine attack that showed "North Korea remains a credible and dangerous threat on the peninsula," the four-star general said.

On a possible new Korean conflict, Scaparrotti issued a dire warning: "If deterrence fails, full-scale conflict in Korea would more closely parallel the high intensity combat of the Korean War than the recent wars in Iraq and Afghanistan. Furthermore, any conflict with North Korea would significantly increase the threat of the use of weapons of mass destruction."

Adm. William Gortney, commander of U.S. Northern Command, which is in charge of U.S. missile defenses, told a Senate hearing last week that North Korea is capable of hitting the United States with a nuclear missile.

"As the commander accountable of holding the trigger to defend the nation against that particular threat, I assess that they have the ability to put an ICBM in space and range the continental United States and Canada," Gortney said, adding that he regards North Korea as having the capability to put a small nuclear warhead on its long-range missiles.

Kim last week was photographed with what he said was a metal sphere identified by the North Koreans as a missile-sized nuclear warhead. Nuclear experts, however, said they doubted the sphere seen in the photograph was an actual warhead.

Adm. Cecil Haney, the commander of the U.S. Strategic Command, testified along with Gortney, warning that North Korea would face a devastating nuclear counterstrike if it were to use nuclear arms.

"I can't tell you exactly what Kim Jong Un, the leader of North Korea, thinks today, this very minute," Haney said. "But he has to know that he faces a very credible response across our joint military forces if he decides to do the unthinkable."

The U.S. military recently deployed two U.S. nuclear-capable B-2 stealth bombers to Asia and keeps nuclear missile submarines within range of North Korea during current times of tensions with North Korea.

Kirby, the State Department spokesman, said Friday that the United States has a wide range of tools to prevent North Korea from conducting additional nuclear tests.

"I wouldn't rule anything in or out at this time," Kirby said. "I'm not gonna speculate about anything that might happen in the future."