There 44 ground-based missile interceptors at Vandenberg Air Force Base in California and Fort Greely in Alaska. Pictured: A rocket launching from Vandenberg last year

Military experts have warned that the US's missile defense system is years out of date and ineffective against North Korea's nuclear-armed ballistic missiles.

The warnings come after President Donald Trump and North Korean dictator Kim Jong-un agreed to have face-to-face talks by the end of May.

According to the White House, Kim has pledged to denuclearize and stop missile testing.

The unprecedented meeting and the concessions made by North Korea in the build-up to it have led President Trump to boast of US strength - but experts have warned of a 'gap' between American defense and its enemies' missiles.

One, former assistant secretary of defense Philip Coyle, told BuzzFeed News that the US's primary missile defense system is simply 'not effective'.

He was referring to the 44 ground-based missile interceptors at Vandenberg Air Force Base in California and Fort Greely in Alaska.

Forty are at Fort Greely and four at Vandenberg, but there is a plan to deploy 20 more in Alaska by 2023.

The unprecedented meeting and the concessions made by North Korea in the build-up to it have led President Trump to boast of US strength - but experts have warned of a 'gap' between American defense and its enemies' missiles. Pictured: Defensive missiles being tested at Vandenberg base in August last year

Forty ground-based missile interceptors are at Fort Greely (pictured) and four at Vandenberg, but there is a plan to deploy 20 more in Alaska by 2023

The warnings come after President Donald Trump and North Korean dictator Kim Jong-un agreed to have face-to-face talks by the end of May

Coyle, however, told BuzzFeed that such a strategy is 'really just throwing good money after bad' given that the system is incapable of guaranteeing US safety.

Defense officials have previously said that destroying incoming missiles by hitting them with other missiles is like trying to 'hit a bullet with another bullet'.

Since 1999, the ground-based missile interception system has knocked out 10 of 18 ballistic targets in testing - despite costing $40 billion.

President Trump has asked for a $2 billion boost to spending on the system, but the wisdom of this move has been called into question given its effectiveness.

Retired Air Force Lt Gen Dan Leaf said the US 'ought not to declare victory' after securing a meeting with Kim.

'The US should seize the moment, and be very aggressive about making progress, he added.

North Korea's leader Kim Jong-un dwarfed by the newly developed intercontinental ballistic rocket Hwasong-15

But none of the improvements to American missile defense is expected to be finished until midway through the next decade - which is particularly bad news given the rapid development of North Korea's technology.

Riki Ellison, of the Missile Defense Advocacy Alliance, said: 'They thought they'd have time to contain that threat until the new systems kicked in around 2023, so there's absolutely a gap there now.'

But Lt Gen Leaf said: 'You can't bet everything on missile defense', and stressed that the US is 'not going to achieve perfection'.

Retired Air Force Lt Gen Dan Leaf said the US 'ought not to declare victory' after securing a meeting with Kim

Other considerations include diplomacy - and whether or not the enemy's missile would actually work.

'Combine all those probabilities and you've got a pretty good bet on countering such an attack,' Lt Gen Leaf said, adding that the probability of defending against an attack is not 100 per cent - but is at a level he is 'pretty comfortable' with.

Meanwhile, the UN said any progress in the nuclear and security dialogue with North Korea must be accompanied by discussions on human rights violation.

'Today, we witness what appears to be a potential for rapid progress on the political and security front, with communication channels steadily building up between the two Koreas as well as the United States of America, and historical summits plans for the future,' Tomas Ojea Quintana, UN special rapporteur on human rights in the Democratic People's Republic of Korea (DPRK), told the world body's Human Rights Council.

But he added: 'Let me urge the DPRK to consolidate this rapprochement with a parallel opening to human rights review. My main message today is that any advancement on the security dialogue should be accompanied by a parallel expansion on the human rights dialogue.'