U.S. President Donald Trump says he wants to build up the U.S. nuclear arsenal to ensure it is at the "top of the pack," saying the United States has fallen behind in its atomic weapons capacity. 

In an interview with Reuters, Trump also said China could solve the national security challenge posed by North Korea "very easily if they want to," ratcheting up pressure on Beijing to exert more influence to rein in Pyongyang's increasingly bellicose actions.

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American conservatives heard Trump reiterate his election promises as he spoke on the third day of the four-day forum, held at the convention centre in Oxon Hill, Md., a suburb of Washington. (Jonathan Ernst/Reuters)

In his first comments about the U.S. nuclear arsenal since taking office on Jan. 20, Trump said the U.S. has "fallen behind on nuclear weapon capacity."

"I am the first one that would like to see everybody — nobody have nukes, but we're never going to fall behind any country even if it's a friendly country, we're never going to fall behind on nuclear power. 

"It would be wonderful, a dream would be that no country would have nukes, but if countries are going to have nukes, we're going to be at the top of the pack," Trump said.

The new strategic arms limitation treaty, known as New START, between the U.S. and Russia requires that by Feb. 5, 2018, both countries must limit their arsenals of strategic nuclear weapons to equal levels for 10 years. 

The treaty permits both countries to have no more than 800 deployed and non-deployed land-based intercontinental and submarine-launched ballistic missile launchers and heavy bombers equipped to carry nuclear weapons, and contains equal limits on other nuclear weapons. 

Analysts have questioned whether Trump wants to abrogate New START or would begin deploying other warheads. 

'One-sided deal'

In the interview, Trump called New START "a one-sided deal."

"Just another bad deal that the country made, whether it's START, whether it's the Iran deal.… We're going to start making good deals," he said. 

The U.S. is in the midst of a $1-trillion, 30-year modernization of its aging ballistic-missile submarines, bombers and land-based missiles, a price tag that most experts say the country cannot afford.

Trump complained that Russia's reported deployment of a ground-based cruise missile is in violation of a 1987 treaty that bans land-based American and Russian intermediate-range missiles. 

"To me it's a big deal," Trump said. 

Asked if he would raise the issue with Putin, Trump said he would do so "if and when we meet." He said he had no meetings scheduled as of yet with Putin. 

Speaking from behind his desk in the Oval Office, Trump declared that "we're very angry" at North Korea's ballistic 
missile tests and said accelerating a missile defence system for U.S. allies Japan and South Korea was among many options available. 

"There's talks of a lot more than that," Trump said, when asked about the missile defence system. "We'll see what happens. But it's a very dangerous situation, and China can end it very quickly in my opinion."