China has announced it will limit oil supplies to North Korea under UN sanctions, stepping up pressure on Pyongyang over its pursuit of nuclear and missile technology.

The Commerce Ministry said on Saturday that China, the North's main trading partner and energy supplier, will limit supplies of refined petroleum products starting on October 1.

It said Beijing will also ban imports of North Korean textiles, one of Pyongyang's last major sources of foreign revenue following repeated rounds of UN sanctions.

China has long been the North's only major ally and diplomatic protector but is expressing increasing frustration with the government of Kim Jong Un. Beijing's status as the North's main trading partner makes its cooperation critical to the success of economic sanctions.

Earlier US president Donald Trump lashed out at Kim during a rally speech in Alabama.

Mr Trump said: "We can't have madmen out there shooting rockets all over the place", adding: "Rocket Man should have been handled a long time ago".

Both leaders have been trading barbs.

Kim earlier this week called Mr Trump "deranged" and said he would "pay dearly" for his threats.

Mr Trump delivered a combative speech on Tuesday at the UN General Assembly, where he mocked Kim as a "Rocket Man" on a "suicide mission". Mr Trump also told the UN that if "forced to defend itself or its allies, we will have no choice but to totally destroy North Korea".