South Korea launched interceptor rockets built to down North Korea's missiles just hours after Kim Jong-un issued a 'stern warning' to the US saying he could hit New York.

The North Korean leader said Saturday the second flight test of an intercontinental ballistic missile on Friday demonstrated his country can hit the US mainland.

Had it been fired at a standard trajectory, the rocket could have reached Los Angeles, Denver and Chicago and would have even had New York and Boston within its sights, according to analysts.

In response, South Korea and the US teamed up to fire their anti-missile defence system, which would be deployed should Kim Jong-un attempt to fire a nuclear weapon over the Pacific.

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Trump said the weapons and tests 'further isolate North Korea, weaken its economy, and deprive its people.' He vowed to 'take all necessary steps' to ensure the security of the U.S. and its allies. Pictured: Today US and South Korea's response to Kim's launch today

In a show of force against the dictator and his military, the United States and South Korea held a joint missile exercise in response. Pictured: South Korea's Hyunmu-2 Missile System and US Army Tactical Missile System firing missiles into the East Sea

The US and South Korea fired missiles into the East Sea from an undisclosed location on South Korea's east coast during a South Korea-US joint missile drill aimed to counter North Korea's ICBM test (pictured)

Kim expressed 'great satisfaction' after the Hwasong-14 missile reached a height of 2,314 miles and traveled 620 miles before accurately landing in waters off Japan.

The test was aimed at confirming the maximum range and other technical aspects of the missile it says was capable of delivering a 'large-sized, heavy nuclear warhead.'

Pyongyang's continuing development of nuclear weapons is a growing cause of concern for leaders in the United States, South Korea and Japan.

In a show of force against the dictator and his military, the United States and South Korea held the joint missile exercise in response.

South Korean Defense Minister Song Young-moo called for the deployment of the strategic US military assets — which usually means stealth bombers and aircraft carriers — as well as additional launchers of an advanced US anti-missile system.

Donald Trump released a statement yesterday after the missile launch, saying: 'North Korea’s test launch yesterday of another intercontinental ballistic missile—the second such test in less than a month—is only the latest reckless and dangerous action by the North Korean regime.

'The United States condemns this test and rejects the regime’s claim that these tests—and these weapons—ensure North Korea’s security. In reality, they have the opposite effect.

'By threatening the world, these weapons and tests further isolate North Korea, weaken its economy, and deprive its people.

'The United States will take all necessary steps to ensure the security of the American homeland and protect our allies in the region.'

North Korea now has the capability to reach Los Angeles and Chicago with its missiles, experts claimed on Friday, following the country's second ICBM launch of the month

Kim Jong-Un is reportedly greatly satisfied with the successful launch that was meant to give the United States a 'stern warning', according to reports on Saturday

Meanwhile the Japanese government spokesman Yoshihide Suga said the missile, launched late Friday night, flew for about 45 minutes — about five minutes longer than the first.

The rocket was launched on very high trajectory, which limited the distance it traveled, and landed west of Japan's island of Hokkaido.

Although Kim Jong-un hasn't expressed a strong desire to attack mainland Europe, the new analysis would suggest London, Paris, Berlin and Rome are all within range although the missiles would have to soar above land as opposed to the Pacific and negotiate the earth's rotation.

David Wright from the Union of Concerned Scientists said: 'Based on current information, Friday’s missile test by North Korea could easily reach the US West Coast and a number of major US cities.'

How far would missile have to travel from Pyongyang to reach the US and Europe? US Naval Base in Guam: 2,114 miles Hawaii: 4,727 miles San Francisco: 5,588 miles Los Angeles: 5,935 miles New York: 6,783 miles Washington, DC: 6,857 miles Rome: 5,449 miles Paris: 5,446 miles London: 5,379 miles Berlin: 4,926 miles Advertisement

The ICBM was launched at a lofted trajectory allowing it to fall in the Sea of Japan with a ground range of around 600 miles.

Reports suggest the maximum altitude of the launch was 2,300 miles and that it flew for 47 minutes.

Mr Wright added: 'If those numbers are correct, the missile flown on a standard trajectory the missile would have a range 10,400 km (6,500 miles), not taking into account the Earth’s rotation.

'However, the rotation of the Earth increases the range of missiles fired eastward, depending on their direction.

'It is important to keep in mind that we do not know the mass of the payload the missile carried on this test.

'If it was lighter than the actual warhead the missile would carry, the ranges would be shorter than those estimated above.'

The state-run Korean Central News Agency (KNCA) made the report of Kim's pleasure of the successful launch.

North Korea launched a missile that came 'threateningly' close to Japan on Friday night, which has prompted the country's prime minster to admonish the isolated nation.

Analysts had estimated that North Korea's first ICBM on July 4 could have reached Alaska, and said that the latest missile appeared to extend that range significantly.

Immediately after the launch, US and South Korean forces conducted live-fire exercises.

North Korea launched a missile (pictured) that came 'threateningly' close to Japan on Friday night, which has prompted the country's prime minster to admonish North Korea

North Koreans watch a news broadcast on a missile launch in Pyongyang on Saturday

North Korean citizens cheered as they watched the country's second successful launch of an ICBM this month

The KCNA quoted Kim as saying that the launch reaffirmed the reliability of the country's ICBM system and an ability to fire at 'random regions and locations at random times' with the 'entire' US mainland now within range.

The agency said that the test confirmed important features of the missile system, such as the proper separation of the warhead and controlling its movement and detonation after atmospheric re-entry.

Kim said the launch sent a 'serious warning' to the United States, which has been 'meaninglessly blowing its trumpet' with threats of war and stronger sanctions, the KCNA said.

The North Korean flight data was similar to assessments by the United States, South Korea and Japan.

David Wright, a physicist and co-director of the global security program at the Union of Concerned Scientists, said that if reports of the missile's maximum altitude and flight time are correct, it would have a theoretical range of at least 6,500 miles.

That means it could have reached Los Angeles, Denver or Chicago, depending on variables such as the size and weight of the warhead that would be carried atop such a missile in an actual attack.

Intercontinental ballistic missile (ICBM) Hwasong-14 is pictured during its second test-fire in this undated picture provided by KCNA in Pyongyang

An expert said if reports of the missile's maximum altitude and flight time are correct, it would have a theoretical range of at least 6,500 miles, which could reach Chicago

The nightmare scenario for the Pentagon is a missile capability that puts the East Coast - Washington DC and New York City - within range.

Some experts fear that North Korea may be even able to do that, reported Vox.

President Donald Trump issued a statement condemning the missile test as a threat to the world, and rejecting North Korea's claim that nuclear weapons ensure its security. 'In reality, they have the opposite effect,' he said.

Trump said the weapons and tests 'further isolate North Korea, weaken its economy, and deprive its people.' He vowed to 'take all necessary steps' to ensure the security of the US and its allies.

Washington and its allies have watched with growing concern as Pyongyang has made significant progress toward its goal of having all of the US within range of its missiles to counter what it labels as US aggression.

While there are hurdles, including building nuclear warheads to fit on those missiles and ensuring reliability, many analysts have been surprised by how quickly Kim Jong-un has developed North Korea's nuclear and missile programs.

This comes despite several rounds of UN Security Council sanctions that have squeezed the impoverished country's economy.

Trump has said he will not allow North Korea to obtain an ICBM that can deliver a nuclear warhead.

But this week, the Defense Intelligence Agency reportedly concluded that the North will have a reliable ICBM capable of carrying a nuclear weapon as early as next year, in an assessment that trimmed two years from the agency's earlier estimate.

Japanese Prime Minister Shinzo Abe (pictured) called North Korea's missile launch a 'serious and real threat' to the country's security

North Korean leader Kim Jong-Un inspecting the test-fire of intercontinental ballistic missile Hwasong-14 at an undisclosed location earlier this month

Japanese Prime Minister Shinzo Abe called the launch a 'serious and real threat' to the country's security.

Suga, the Japanese spokesman, said Japan has lodged a strong protest with North Korea. 'North Korea's repeated provocative acts absolutely cannot be accepted,' he said.

The French Foreign Ministry condemned the launch and called for 'strong and additional sanctions' by the United Nations and European Union.

'Only maximal diplomatic pressure might bring North Korea to the negotiating table,' the ministry said in a statement.

And the country's UN Ambassador Francois Delattre said: 'This is a 4G threat - global, grave, given and growing.

'That's why we call for a firm and quick reaction including the adoption of strong additional sanctions by the Security Council.'

Pictured: What officials believe to have been the route taken by the missile after it was launched from North Korea

A spokesman for Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, said that Dunford met at the Pentagon with the commander of U.S. forces in the Pacific, Adm. Harry Harris, to discuss U.S. military options in light of North Korea's missile test.

The spokesman, Navy Capt. Greg Hicks, said Dunford and Harris placed a phone call to Dunford's South Korean counterpart, Gen. Lee Sun Jin. Dunford and Harris 'expressed the ironclad commitment to the U.S.-Republic of Korea alliance,' Hicks said, referring to the U.S. defense treaty that obliges the U.S. to defend South Korea.

Abe, too, said Japan would cooperate closely with the U.S., South Korea and other nations to step up pressure on North Korea to halt its missile programs.

The Hwasong 14 ICBM test-fired earlier this month was also launched at a very steep angle, a technique called lofting, and reached a height of more than 2,500 kilometers (1,550 miles) before splashing down in the ocean 930 kilometers (580 miles) away. Analysts said that missile could be capable of reaching most of Alaska or possibly Hawaii if fired in an attacking trajectory.

South Korea's Joint Chiefs of Staff said the missile was launched from North Korea's northern Jagang province near the border with China. President Moon Jae-in presided over an emergency meeting of the National Security Council, which called for an emergency meeting of the U.N. Security Council and stronger sanctions on North Korea.

July 27 is a major national holiday in North Korea called Victory in the Fatherland Liberation War Day, marking the day when the armistice was signed ending the 1950-53 Korean War. That armistice is yet to be replaced with a peace treaty, leaving the Korean Peninsula technically in a state of war.

In spite of the surge of launches, there is some skepticism surrounding figures coming from North Korea.

Just this week, Kim Jong-un's flagship intercontinental ballistic missiles were branded too small to hit the US with a meaningful payload, according to a team of experts.

After striking fear around the world with the rocket launch on July 4 after a string of similar operations, it appears North Korea's nuclear threat may not be not all it seems.

Scientists analysing the potential threat of the ICBMs said the missiles would be effectively useless even if they managed to reach America.

Ralph Savelsberg and James Kiessling, writing in Breaking Defense, looked at the KN-14 or the Hwasong-14 - North Korea's flagship missile.

At full range, they said the ICBM's accuracy was so bad that it would only be able to land around 19 miles from its intended target.

The authors said: 'Capabilities exceed the arbitrary 5,500 km range value, but it’s not really a useful ICBM.

'It’s too small and too close to zero payload at useful ranges.'

This means the rocket might be able to travel thousands of miles, but once it got to the end of its journey it would be rendered useless.