North Korea said on Saturday it has successfully tested a new intercontinental ballistic rocket engine that will give it the ability to stage nuclear strikes on the United States. The engine’s ground test, if true, would be a big step forward for the North’s nuclear weapons programme, which saw its fourth atomic test earlier this year. But the North may still need a good deal of work before it can hit the US mainland with nuclear missiles. South Korean officials say North Korea doesn’t yet have a reliable intercontinental ballistic missile, let alone the ability to arm it with a nuclear warhead. The test, announced by the North’s official Korean Central News Agency, is only the latest in a string of what Washington and its allies consider North Korean provocations, including last month’s launch of a medium-range ballistic missile that violated UN Security Council resolutions that prohibit any ballistic activities by North Korea.