|Experts say the North Korean missile launched in July is capable of reaching US cities|
China says it will stop importing North Korean coal, iron ore, fish and other goods in September as it implements UN sanctions.The UN Security Council, including China, backed a new resolution last weekend imposing fresh sanctions on the rogue state in retaliation for its controversial nuclear programme.
The sanctions aim to block $1bn worth of North Korean exports - about a third of its total exports.
The Chinese government said the imports would stop on 5 September.
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It came as US Joint Chiefs of Staff Chairman Joseph Dunford said military options were being prepared against the North if diplomatic and economic sanctions failed.
The office of South Korean President Moon Jae-in said Mr Dunford had made the comments in a 50-minute meeting to discuss North Korean provocation.
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Tensions have increased over fears North Korea is close to achieving its goal of putting the mainland US within range of a nuclear weapon.
North Korea has threatened to fire missiles into waters off the coast of the US overseas territory of Guam, in the Pacific.
It said the launch would coincide with annual drills involving US and South Korean forces, taking place later this month.
The North's state news agency said about 3.5 million students and workers had volunteered to fight alongside the military to defend their country from the US.
China, meanwhile, has appointed a new special envoy for the North Korean issue.
China is the country's closest ally, but has been angered by its missile tests and repeatedly pressured and berated by President Trump, who wants it to be far tougher on its neighbour.
President Xi has urged restraint and told Washington and Pyongyang to avoid words or actions that could worsen the situation.
South Korean President has also called for a peaceful solution, saying there must not be another war on the Korean Peninsula.