The group has also warned of “significant progress” in Kim Jong-un’s nuclear weapons programme, which it says are advanced enough to target the mainland United States with an “inaccurate but successful” strike.
This comes as US bombers escorted by stealth fighter jets have flown several missions close to North Korea in recent weeks.
American airforce chiefs have said they intend to continue flying sorties in international airspace, despite a warning from the hermit state that they “reserved the right” to shoot them down.
Dictator Kim has relentlessly persisted in his nuclear weapons and long-range ballistic missile programmes despite widespread international condemnation and a series of crippling sanctions.
The DEFCON Warning System’s latest report says: “Tension in the Korean theatre continues to be very high.
“A review of the data coming out of North Korea indicate a country that feels it is being backed into a corner.
“This significantly raises the possibility of a strike as North Korea may believe it either has nothing to lose or is responding to an impending attack.
“The United States exacerbates the situation with hostile language of its own.”
Donald Trump has been embroiled in a bitter war of words with despot Kim, with neither side seemingly willing to back down.
The President tweeted earlier this month that his chief diplomat, Secretary of State Rex Tillerson, was “wasting his time” trying to negotiate with Kim, before adding: “Save your energy Rex, we’ll do what has to be done.”
Mr Trump has previously mocked Kim as “little rocket man” - a reference to his ballistic missile tests - and threatened to “totally destroy” North Korea if it dares attack the United States or one of its allies.
In response, Kim branded the President a “mentally deranged US dotard”.
And North Korean Foreign Minister Ri Yong-ho told reporters last month the President’s words amounted to a declaration of war.
He said: “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 DEFCON Warning System says the US is actively discouraging any talks with the secretive state, and claims “all backchannel dialog with North Korea has ended”.
Because of the top-secret nature of North Korea’s nuclear and missile programmes, it is impossible to say exactly what Kim’s capabilities are.
Analysts believe the rogue state has developed an intercontinental ballistic missile (ICBM), and miniaturised a nuclear weapon to fit on it, though there is debate over how accurate its current arsenal is.
But in its latest report, DEFCON Warning System says, even if Kim does not have the capability of targeting a specific city or area accurately, his ICBMs are still capable of hitting the mainland United States.
It says: “The International Atomic Energy Agency says North Korea has made significant progress in its nuclear program and that it poses a new level of threat to the international community.
“While many experts do not believe that North Korea yet possesses the ability to strike the United States directly, the DEFCON Warning System points out that the experts are assessing the accuracy and success rate of such an attack.
“DEFCON Warning System continues to warn that an inaccurate strike is still a successful strike.”
However the latest report says: “There are currently no imminent nuclear threats against the United States at this time.”
It concludes that the current threat of nuclear war is level four out of five. Level one is the highest, and if used by the US military would mean nuclear war was imminent.
The DEFCON Warning System in a private intelligence organisation which gathers the latest publicly available information on a potential nuclear conflict from across the United States.
The group also says it has some contacts within the US Government and military agencies.
It is not the same as the official, classified US military DEFCON rating, which is short for defence readiness condition.