The United States intends to bolster its west coast’s missile defences to counter a growing nuclear threat from North Korea and Iran.

At a press conference in Washington, DC, Defence Secretary Chuck Hagel announced plans to add 14 missile interceptors to a site in Alaska, and establish a radar tracking system based in Japan.

The interceptors, which can shoot down enemy missiles in the air before they reach the US, will be added to 30 existing ground-based interceptors in Alaska and California, by 2017. Announcing the $1 billion (£660 million) plans, Mr Hagel described North Korea’s recent anti-American pronouncements as “irresponsible and reckless provocations.”

Download the new Independent Premium app Sharing the full story, not just the headlines

Last month, North Korea launched its third nuclear test. After the UN Security Council stepped up its sanctions, the Pyongyang government threatened a pre-emptive nuclear strike on South Korea and the US. One of the country’s top generals has claimed that the country possesses nuclear-tipped intercontinental ballistic missiles that are ready to be launched. Whether those missiles have the capacity to reach the continental US, more than 3,000 miles away, is another matter. President Barack Obama told ABC News earlier this week that he did not believe North Korea had the capability to carry out its threats.

The existing missile defence sites at Fort Greely, Alaska and Vandenberg Air Force Base, California were built in response to the threat of North Korean missile strikes during George W Bush’s presidency. The US Navy has also beefed up its missile defence, deploying four guided missile destroyers close to the Korean peninsula. Speaking on Tuesday, US Defence Undersecretary James Miller said, “Our policy is to stay ahead of the threat, and to continue to ensure that we are ahead of any potential future Iranian or North Korean ICBM capability.''

Iran, meanwhile, is said to be at least a year from developing a functioning nuclear weapon. On Thursday evening, as he prepared for his first presidential visit to Israel, Mr Obama told Tel Aviv’s Channel 2 News that the US would not stand by while Tehran acquired nuclear capabilities. “I have been crystal clear about my position on Iran possessing a nuclear weapon,” he said. “That is a red line for us. It is not only something that would be dangerous for Israel, it would be dangerous for the world.”