The US and China agreed to cooperate on tackling North Korea’s nuclear weapons programme in a phone call between their top diplomats. The two countries agreed to implement the “new, robust and comprehensive” sanctions regime against North Korea adopted by the United Nations last month, Nikki Haley, US ambassador to the UN, said. The call on Friday came as Pyongyang has been threatening retaliation against Washington over new US sanctions. Ms Haley said the US delegation would work to make the UN’s strongest economic sanctions package ever against North Korea permanent. The sanctions were designed to further isolate North Korea over its nuclear and ballistic missile programmes. China has tried to use its influence with Pyongyang to bring it back to the negotiating table. US President Donald Trump said on Friday that his top diplomat “discussed the full range of grave threats facing our country and the rest of the world”. The White House also said Mr Trump and his Chinese counterpart, Xi Jinping, had “agreed that North Korea must stop its provocative and escalatory behaviour”. ‘Harsh sanctions’ North Korean leader Kim Jong-un urged the country to improve its defence capabilities Ms Haley announced new sanctions just days after North Korea fired a missile over the northern Japanese island of Hokkaido. The test missile, with an expected range of more than 1,100km (680 miles), splashed into the sea and failed in its third and final stage. “The clock has now run out, and all options are on the table,” she said. “The United States is prepared to use the full range of our capabilities to defend ourselves and our allies.” At the same time, the US will work with China to adopt the strongest UN Security Council sanctions yet against Pyongyang, she added. “The unanimous adoption of this resolution last month sends a clear message to North Korea that the world is united, we’re united in our resolve, we’re united in our commitment to stopping the advancement of this illegal program,” she said. US officials said they were working closely with Beijing and Moscow to develop a plan to implement further sanctions. A US official said on Friday that despite growing cooperation between the US and South Korea, its northern neighbour still posed a threat and was a global problem. “It is something that concerns us not only because it is obviously a threat to the South Korea and Japan, but it is a problem for the world at large,” said the US official, speaking on condition of anonymity. South Korea and the US are planning to deploy the Terminal High Altitude Area Defence (Thaad) anti-missile system in South Korea, a US defence official said on Friday. In her remarks, Ms Haley said the Thaad system was a defensive measure, adding that “any attack on the United States or its allies will be defeated and any use of nuclear weapons will be met with a response that is effective and overwhelming”. ‘Escalate response’ Earlier this week, North Korea threatened to attack the US territory of Guam, which hosts two American air bases, if it continued to pressure Pyongyang to curb its missile tests. North Korea regularly threatens to destroy South Korea and its main ally, the United States, as well as Japan. It says the programmes are necessary to counter US aggression. Mr Trump and Mr Xi spoke by telephone on Thursday, hours after South Korea had said it was in touch with the North over a plan to hold talks at a border village in North Korea. Mr Trump said he and Mr Xi agreed that North Korea must stop its “provocative” and “escalatory” behaviour. China is by far the most important trading partner for North Korea, with around 80% of its trade passing through China. North Korea has repeatedly expressed anger over US-South Korea military exercises, which it sees as preparations for war. In recent months, it has also conducted a series of high-profile tests of military hardware, including two intercontinental ballistic missile tests. Its most powerful nuclear test to date, which it claims was a hydrogen bomb, was conducted in September. The US has also taken an increasingly hard line on North Korea’s nuclear weapons programme, with its most recent annual report to Congress saying it was “highly likely” that North Korea had attained the capability to deliver a nuclear weapon with intercontinental ballistic missile.