China has announced a series of sanctions against North Korea.

The country has restricted imports of North Korean coal and sales of jet fuel under UN sanctions.

The Security Council passed a resolution in March, which expanded UN sanctions aimed at withholding funds for the North's nuclear and ballistic missile programmes. It came after Pyongyang conducted four tests in recent months.

Among the North Korean materials to be banned, some of which are fundamental to the country's revenue, are coal, iron, iron ore, gold, titanium and rare earths.

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While China's restrictions allow some North Korean materials to be imported for civilian use, any trade connected to the North's missile or nuclear programmes has been prohibited. For the UN sanctions to succeed, the cooperation of China - an ally of North Korea - has been viewed as essential.

The move by China comes after the global Nuclear Security Summit held in Washington last week. There, at a meeting between Barack Obama and Chinese President Xi Jinping, the US President said both countries were “committed to the [denuclearisation] of the Korean Peninsula”.

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Mr Xi said: “China and the US have a responsibility to work together.”

After the vote on the resolution, drafted by the US and China, US Ambassador Samantha Power said the sanctions were the toughest yet, Reuters reported.

"Virtually all of the DPRK's (North Korea) resources are channelled into its reckless and relentless pursuit of weapons of mass destruction," she said.

UN sanctions have been imposed on North Korea since 2006 because of the country's nuclear tests and rocket launches.